SUMMARY OF THE FUND

Investment Objective

The Fund seeks to provide investors with long term capital appreciation.

Fees and Expenses of the Fund:

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Class A Shares of the Fund. More information about these and other discounts is available from your financial professional and in the section entitled “Classes of Shares” herein on page 11 of the Prospectus.

Expense Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

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The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year, and the Fund’s operating expenses remain the same (taking into account the expense limitation agreement until April 30, 2016 with respect to Class I Shares). Although your actual costs may be higher or lower, based on these assumptions your costs would be:

You would pay the following expenses if you did not redeem your shares of the Fund:

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in the annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 12% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 65% of its total assets in equity securities of foreign issuers located in at least three countries outside the United States that Gabelli Funds, LLC, the Fund’s investment adviser (the “Adviser”) believes are likely to have rapid growth in revenues and earnings and potential for above-average capital appreciation. Equity securities include common and preferred stocks, securities convertible into common stocks and securities such as rights and warrants that have common stock characteristics. The Fund seeks to invest in companies that have the potential to grow faster than other companies in their respective equity markets and are priced at attractive valuation levels.

The Fund intends to diversify its investments across different countries. The percentage of Fund assets invested in particular countries or regions will change from time to time based on the Adviser’s judgment. The Fund intends to invest in the securities of companies located in developed countries and, to a lesser extent, those located in emerging markets.

The Adviser may sell a holding if its fundamentals deteriorate or change in a way, as determined by the Adviser, that the investment case for the holding is no longer appropriate for the Fund.

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Principal Risks

You May Want to Invest in the Fund if:

The Fund’s share price will fluctuate with changes in the market value of the Fund’s portfolio securities. Your investment in the Fund is not guaranteed; you may lose money by investing in the Fund. When you sell Fund shares, they may be worth more or less than what you paid for them.

The principal risks presented by the Fund are:

Performance

The bar chart and table that follow provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year, and by showing how the Fund’s average

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annual returns for one year, five years, and ten years compared with those of a broad based securities market index and an additional style specific index. As with all mutual funds, the Fund’s past performance (before and after taxes) does not predict how the Fund will perform in the future. Updated information on the Fund’s results can be obtained by visiting www.gabelli.com.

GAMCO INTERNATIONAL GROWTH FUND, INC.

(Total Returns for Class A Shares for the Years Ended December 31)

Sales loads are not reflected in the above chart. If sales loads were reflected, the Fund’s returns would be less than those shown.

During the calendar years shown in the bar chart, the highest return for a quarter was 21.18% (quarter ended June 30, 2009) and the lowest return for a quarter was (23.57)% (quarter ended September 30, 2008).

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The returns shown for Class I Shares prior to their first issuance dates are those of the Class AAA Shares of the Fund, which are not offered in this Prospectus. All classes of the Fund would have substantially similar annual returns because the shares are invested in the same portfolio of securities and the annual returns would differ only to the extent that the classes do not have the same expenses.

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than “Return Before Taxes” because the investor is assumed to be able to use the capital loss from the sale of Fund shares to offset other taxable gains. Actual after-tax returns depend on the investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax deferred arrangements, such as 401(k) plans or Individual Retirement Accounts, including “Roth” IRAs and SEP IRAs (collectively, “IRAs”). After-tax returns are shown only for Class A Shares. After-tax returns for other classes will vary due to the differences in expenses.

Management

The Adviser. Gabelli Funds, LLC serves as the Adviser to the Fund.

The Portfolio Manager. Mr. Caesar M.P. Bryan, Senior Vice President and Portfolio Manager with GAMCO Asset Management, Inc., has served as Portfolio Manager of the Fund since its inception in 1995.

Purchase and Sale of Fund Shares

The minimum initial investment for Class A and Class C Shares must be at least $1,000 ($250 for IRAs or “Coverdell” Education Savings Plans.) There is no minimum initial investment in an automatic monthly investment plan. There is no minimum for subsequent investments.

Your minimum initial investment for Class I Shares must be at least $500,000. The minimum initial investment for Class I Shares is waived for employee benefit plans with assets of at least $50 million.

You can purchase or redeem the Fund’s shares on any day the New York Stock Exchange (“NYSE”) is open for trading (a “Business Day”). You may purchase or redeem Fund shares by written request via mail (The Gabelli Funds, P.O. Box 8308, Boston, MA 02266-8308), by personal or overnight delivery (The Gabelli Funds, c/o BFDS, 30 Dan Road, Canton, MA 02021-2809), by bank wire, or by Automated Clearing House (“ACH”) system.

You may also redeem Fund shares by telephone at 800-GABELLI (800-422-3554), on the Internet at www.gabelli.com, or through an automatic cash withdrawal plan.

You can also place orders to purchase or sell Fund shares through registered broker-dealers or other financial intermediaries that have entered into appropriate selling agreements with G.distributors, LLC, the Fund’s distributor (“G.distributors” or the “Distributor”). The broker-dealer or other financial intermediary will transmit these transaction orders to the Fund on your behalf and send you confirmation of your transactions and periodic account statements showing your investments in the Fund.

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Tax Information

The Fund expects that distributions will generally be taxable as ordinary income or long term capital gains to taxable investors, unless you are investing through a tax deferred arrangement, such as a 401(k) plan or an IRA.

Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase the Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund and its related companies may pay the intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary’s website for more information.

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INVESTMENT OBJECTIVE, INVESTMENT STRATEGIES, AND RELATED RISKS

The Fund seeks to provide long term capital appreciation. The production of any current income is incidental. To achieve its investment objective, the Fund invests primarily in the equity securities of foreign issuers. The investment objective of the Fund is fundamental and may not be changed without shareholder approval.

Under normal circumstances, the Fund will invest at least 65% of its total assets in the equity securities of foreign issuers located in at least three countries outside the United States that the Adviser believes are likely to have rapid growth in revenues and earnings and potential for above-average capital appreciation.

In selecting investments for the Fund, the Adviser considers a number of factors, including:

The Fund intends to diversify its investments across different countries, but the percentage of Fund assets invested in particular countries or regions will change from time to time based on the Adviser’s judgment. The Fund intends to invest in the securities of companies located in developed countries and, to a lesser extent, those located in emerging markets.

An important function of the Adviser’s investment process is to establish through the Adviser’s research a value at which a particular stock may be sold, provided there are no other fundamental changes in the business. The Adviser constantly monitors the Fund’s holdings to determine if such holdings continue to act in accordance with the factors described above and the Fund’s investment objective. The Adviser may sell a holding if its fundamentals deteriorate or change in a way, as determined by the Adviser, that the investment case for the holding is no longer appropriate for the Fund.

The Fund may also use the following investment technique:

The Fund may also engage in other investment practices in order to achieve its investment objective. These are discussed in the Statement of Additional Information (“SAI”), which may be obtained by calling 800-GABELLI (800-422-3554), your financial intermediary, or free of charge through the Fund’s website at www.gabelli.com.

Investing in the Fund involves the following risks:

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Portfolio Holdings.    A description of the Fund’s policies and procedures with respect to the disclosure of the Fund’s portfolio securities is available in the SAI.

MANAGEMENT OF THE FUND

The Adviser.    Gabelli Funds, LLC, with its principal offices located at One Corporate Center, Rye, New York 10580-1422, serves as investment adviser to the Fund. The Adviser makes investment decisions for the Fund and continuously reviews and administers the Fund’s investment program and manages the Fund’s operations under the general supervision of the Fund’s Board of Directors (the “Board”). The Adviser also manages several other open-end and closed-end investment companies in the Gabelli/GAMCO family of funds. The Adviser is a New York limited liability company organized in 1999 as successor to GGCP, Inc., a New York corporation originally organized in 1980. The Adviser is wholly owned subsidiary of GAMCO Investors, Inc. (“GBL”), a publicly held company listed on the NYSE.

As compensation for its services and the related expenses borne by the Adviser for the fiscal year ended December 31, 2014, the Fund paid the Adviser a fee computed daily and payable monthly in an amount equal on an annualized basis to 1.00% of the value of its average daily net assets. The Adviser has contractually agreed to waive its investment advisory fees and/or reimburse expenses to the extent necessary to maintain Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement (excluding brokerage, acquired fund fees and expenses, interest, taxes, and extraordinary expenses) at no more than 1.00% for the Fund’s Class I Shares. The fee waiver and expense reimbursement agreement will continue until at least April 30, 2016, and may not be terminated by the Adviser before such date. In addition, the Fund has agreed, during the three year period following any waiver or reimbursement by the Adviser, to reimburse the Adviser for any such amounts to the extent, after giving effect to the repayment, such adjusted Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement would not exceed 1.00% on an annualized basis for Class I Shares.

The Fund’s semiannual report to shareholders for the period ended June 30, 2014 contains a discussion of the basis of the Board’s determination to continue the Investment Advisory Agreement as described above.

The Portfolio Manager.    Mr. Caesar M.P. Bryan has been primarily responsible for the day to day investment management of the Fund since June 1995. Mr. Bryan is a Senior Vice President and Portfolio Manager with GAMCO Asset Management Inc., a wholly owned subsidiary of GBL. He has been a Portfolio Manager of The GAMCO Global Growth Fund and the Gabelli Gold Fund, Inc. since 1994, and The GAMCO Global Opportunity Fund since May 1998. Mr. Bryan has also been a Co-Lead Portfolio Manager of GAMCO Global Gold, Natural Resources & Income Trust since March 2005 and The GAMCO Natural Resources, Gold & Income Trust since January 2011.

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The SAI provides additional information about Mr. Bryan’s compensation, other accounts managed by him, and his ownership of securities in the funds he manages.

INDEX DESCRIPTIONS

The Morgan Stanley Capital International EAFE Index (“MSCI EAFE Index”) is a widely recognized unmanaged index composed of common stocks from Europe, Australia, Asia, and the Far East. The index figures do not reflect any deductions for fees, expenses, or taxes. You can not invest directly in the MSCI EAFE Index.

The Lipper International Multi-Cap Growth Fund Classification represents the average performance of international equity mutual funds as tracked by Lipper Inc. The classification reflects fees and expenses but does not reflect taxes. You cannot invest directly in the Lipper International Multi-Cap Growth Fund Classification.

CLASSES OF SHARES

Three classes of the Fund’s shares are offered in this Prospectus — Class A Shares, Class C Shares, and Class I Shares. Class AAA Shares are offered in a separate prospectus. The Fund is not designed for market-timers; see the section entitled “Redemption of Shares.” Each class of shares has different costs associated with buying, selling, and holding Fund shares. Your broker or other financial professional can assist you in selecting which class of shares best meets your needs based on such factors as the size of your investments and the length of time you intend to hold your shares.

Class I Shares are available to foundations, endowments, institutions, and employee benefit plans. The minimum investment for Class I Shares is $500,000 if the investor purchases the Shares directly through the Distributor or brokers that have entered into selling agreements with the Distributor specifically with respect to Class I Shares. The minimum investment requirement is waived for plans with assets of at least $50 million. The Distributor or its affiliates may accept investments in Class I Shares from purchasers not listed above or that do not meet these qualification requirements (for plans with assets of less than $50 million that the Distributor or its affiliates in their judgment expect to grow to at least $50 million; for investors whose investments in the Gabelli/GAMCO complex, either alone or aggregated with the investments of their affiliates, exceeds the minimum investment; and for an individual investor whose investments in the Fund, when combined with investments in the Fund by any family members, exceeds the minimum investment). The table that follows summarizes the differences among the classes of shares.

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In selecting a class of shares in which to invest, you should consider:

The following sections include important information about sales charges and sales charge reductions and waivers available to investors in Class A Shares and describes information or records you may need to provide to the Fund or your broker in order to be eligible for sales charge reductions and waivers. Information about sales charges and sales charge reductions and waivers to the various classes of the Fund’s shares is also available free of charge and in a clear and prominent format on our website at www.gabelli.com. You should consider the information below as a guide only, as the decision on which share class is best for you depends on your individual needs and circumstances.

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Sales Charge — Class A Shares.    The sales charge is imposed on Class A Shares at the time of purchase in accordance with the following schedule:

No sales charge is imposed on reinvestment of distributions if you select that option in advance of the distribution.

Breakpoints or Volume Discounts

The Fund offers you the benefit of discounts on the sales charges that apply to purchases of Class A Shares in certain circumstances. These discounts, which are also known as breakpoints, can reduce or, in some instances, eliminate the initial sales charges that would otherwise apply to your Class A Shares investment. Mutual funds are not required to offer breakpoints and different mutual fund groups may offer different types of breakpoints.

Breakpoints or Volume Discounts allow larger investments in Class A Shares to be charged lower sales charges. If you invest $50,000 or more in Class A Shares of the Fund, then you are eligible for a reduced sales charge. Initial sales charges are eliminated completely for purchases of $1,000,000 or more, although a 1% CDSC may apply if shares are redeemed up to and including the last day of the eighteenth month after purchase.

Sales Charge Reductions and Waivers — Class A Shares

Reduced sales charges are available to (1) investors who are eligible to combine their purchases of Class A Shares to receive volume discounts and (2) investors who sign a Letter of Intent (the “Letter”) agreeing to make purchases over time. Certain types of investors are eligible for sales charge waivers.

You may qualify for a reduced sales charge, or a waiver of sales charges, on purchases of Class A Shares. The requirements are described in the following paragraphs. To receive a reduction that you qualify for, you may have to provide additional information to your broker or other service agent. For more information about sales charge discounts and waivers, consult with your broker or other service provider.

Volume Discounts/Rights of Accumulation.    In order to determine whether you qualify for a Volume Discount under the foregoing sales charge schedule, you may combine your new investment and your existing investments in Class A Shares with those of your immediate family (spouse and children under age 21), your and their IRAs, and other employee benefit plans and trusts and other fiduciary accounts for

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your and their benefit. You may also include Class A Shares of any other open-end investment company managed by the Adviser or its affiliates that are held in any of the foregoing accounts. The Fund uses the current net asset value per share (“NAV”) of these holdings when combining them with your new and existing investments for purposes of determining whether you qualify for a Volume Discount.

Letter of Intent.    If you initially invest at least $1,000 in Class A Shares of the Fund and submit a Letter of Intent (“Letter”) to your financial intermediary or the Distributor, you may make purchases of Class A Shares of the Fund during a thirteen month period at the reduced sales charge rates applicable to the aggregate amount of the intended purchases stated in the Letter. The Letter may apply to purchases made up to ninety days before the date of the Letter. If you fail to invest the total amount stated in the Letter, the Fund will retroactively collect the sales charge otherwise applicable by redeeming shares in your account at their then current NAV. For more information on the Letter, call your broker.

Required Shareholder Information and Records.    In order for you to take advantage of sales charge reductions, you or your broker must notify the Fund that you qualify for a reduction. Without notification, the Fund is unable to ensure that the reduction is applied to your account. You may have to provide information or records to your broker or the Fund to verify eligibility for breakpoint privileges or other sales charge waivers. This may include information or records, including account statements, regarding shares of the Fund or shares of any other open-end investment company managed by the Adviser or its affiliates held in:

You should therefore keep copies of these types of records.

Investors Eligible for Sales Charge Waivers.    Class A Shares of the Fund may be offered without a sales charge to: (1) employees of the Distributor and its affiliates, The Bank of New York Mellon (“BNYM”), Boston Financial Data Services, Inc., State Street Bank and Trust Company, the Fund’s Transfer Agent (“State Street” or the “Transfer Agent”), BNY Mellon Investment Servicing (US) Inc. and Soliciting Broker-Dealers, employee benefit plans for those employees and their spouses and minor children of such employees when orders on their behalf are placed by such employees (the minimum initial investment for such purchases is $500); (2) the Adviser, its affiliates and their officers, directors, trustees, general partners, and employees of other investment companies managed by the Adviser, employee benefit plans for such persons and their immediate family when orders on their behalf are placed by such persons (with no required minimum initial investment) — the term “immediate family” for this purpose refers to a person’s spouse, children and grandchildren (adopted or natural), parents, grandparents, siblings, a spouse’s siblings, a sibling’s spouse, and a sibling’s children; (3) any other investment company in connection with the combination of such company with the Fund by merger, acquisition of assets, or otherwise; (4) shareholders who have redeemed shares in the Fund and who wish to reinvest in the Fund, provided the reinvestment is made within forty-five days of the redemption; (5) qualified employee benefit plans established pursuant to Section 457 of the Internal Revenue Code of 1986, as amended that have established omnibus accounts with the Fund or an intermediary; (6) qualified employee benefit plans having more than one hundred eligible employees or a minimum of $1 million in plan assets invested in the Fund; (7) any unit investment trusts registered under the Investment Company

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Act of 1940, as amended, which have shares of the Fund as a principal investment; (8) Investment Advisory clients of GAMCO Asset Management, Inc. and their immediate families; (9) employee participants of organizations adopting the 401(k) Plan sponsored by the Adviser; (10) financial institutions purchasing Class A Shares of the Fund for clients participating in a fee based asset allocation program or wrap fee program which has been approved by the Fund’s Distributor; and (11) registered investment advisers or financial planners who place trades for their own accounts or the accounts of their clients and who charge a management, consulting, or other fee for their services; and clients of such investment advisers or financial planners who place trades for their own accounts if the accounts are linked to the master account of such investment adviser or financial planner on the books and records of a broker or financial intermediary.

Investors who qualify under any of the categories described above should contact their financial intermediary. Some of these investors may also qualify to invest in Class I Shares.

Contingent Deferred Sales Charges

You will pay a CDSC when you redeem:

The CDSC payable upon redemption of Class A Shares or Class C Shares in the circumstances described above is 1.00%. In each case, the CDSC is based on the NAV at the time of your investment or the NAV at the time of redemption, whichever is lower.

The Distributor pays sales commissions of up to 1.00% of the purchase price of Class C Shares of the Fund at the time of sale to brokers and financial intermediaries that initiate and are responsible for purchases of such Class C Shares of the Fund.

You will not pay a CDSC to the extent that the value of the redeemed shares represents reinvestment of distributions or capital appreciation of shares redeemed. When you redeem shares, we will assume that you are first redeeming shares representing reinvestment of distributions, then any appreciation on shares redeemed, and then any remaining shares held by you for the longest period of time. We will calculate the holding period of shares acquired through an exchange of shares of another fund from the date you acquired the original shares of the other fund. The time you hold shares in the Gabelli money market fund, however, will not count for purposes of calculating the applicable CDSC.

We will waive the CDSC payable upon redemptions of shares for:

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Rule 12b-1 Plan.    The Fund has adopted distribution plans under Rule 12b-1 (the “Plans”) for Class A and Class C Shares of the Fund (each, a “Plan”). Under these Plans, the Fund may use its assets to finance activities relating to the sale of its Class A and Class C Shares and the provision of certain shareholder services. To the extent any activity is one that the Fund may finance without a distribution plan, the Fund may also make payments to compensate such activities outside a Plan and not be subject to its limitations.

The Class A Plan authorizes payments by the Fund on an annual basis of 0.25% of its average daily net assets attributable to Class A Shares to finance distribution of its Class A Shares or pay shareholder service fees. The Class C Plan authorizes payments on an annual basis of 0.75% of its average daily net assets attributable to Class C Shares to finance distribution of its Class C Shares and 0.25% for shareholder service fees.

Because the Rule 12b-1 fees are higher for Class C Shares than for Class A Shares, Class C Shares will have higher annual expenses. Because Rule 12b-1 fees are paid out of the Fund’s assets on an on-going basis, over time these fees will increase the cost of your investment and may cost you more than paying other types of sales charges. Due to the payment of Rule 12b-1 fees, long term shareholders may indirectly pay more than the equivalent of the maximum permitted front-end sales charge.

Redemption Fee.    Generally, if you sell or exchange your shares within seven days or less after a purchase, you will be charged a redemption fee of 2.00% of the total redemption amount which is payable to the Fund. See “Redemption of Shares” herein.

PURCHASE OF SHARES

You can purchase Fund shares on any Business Day. You may purchase shares directly through registered broker-dealers or other financial intermediaries that have entered into appropriate selling agreements with the Distributor. In addition, certain investors who qualify may purchase Class I Shares of the Fund directly from the Distributor.

The broker-dealer or other financial intermediary will transmit a purchase order and payment to State Street on your behalf. Broker-dealers or other financial intermediaries may send you confirmations of your transactions and periodic account statements showing your investments in the Fund.

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State Street Bank and Trust Company

ABA #011-0000-28 REF DDA #99046187

Re: GAMCO International Growth Fund, Inc.

Account #                    

Account of [Registered Owners]

If you are making an initial purchase, you should also complete and mail a subscription order form to the address shown under “By Mail.” Note that banks may charge fees for wiring funds, although State Street will not charge you for receiving wire transfers.

Share Price.    The Fund sells its shares based on the NAV next determined after the time as of which the Fund receives your completed subscription order form and your full payment, subject to a front-end sales charge in the case of Class A Shares. See “Pricing of Fund Shares” herein for a description of the calculation of the NAV as described under “Classes of Shares — Sales Charge — Class A Shares.”

Minimum Investments.    Your minimum initial investment must be at least $1,000 for Class A and Class C Shares. See “Retirement Plans/Education Savings Plans” and “Automatic Investment Plan” under “Additional Purchase Information for Class A Shares, Class C Shares, and Class I Shares” regarding minimum investment amounts applicable to such plans.

Your minimum initial investment for Class I Shares must be at least $500,000. The minimum initial investment for Class I Shares is waived for employee benefit plans with assets of at least $50 million.

There is no minimum for subsequent investments. Broker-dealers and financial intermediaries may have different minimum investment requirements.

Voluntary Conversion.    Shareholders may be able to convert shares to Class I Shares of the Fund, which have a lower expense ratio, provided certain conditions are met. This conversion feature is intended for shares held through a financial intermediary offering a fee based or wrap fee program that has an agreement with the Adviser or the Distributor specific for this purpose. In such instances, Class A or Class C Shares may be automatically converted under certain circumstances. Generally, Class C Shares are not eligible for conversion until the applicable CDSC period has expired. Please contact your financial intermediary for additional information. Not all share classes are available through all financial intermediaries.

If shares of the Fund are converted to a different share class of the Fund, the transaction will be based on the respective NAV of each class as of the trade date of the conversion. Consequently, a shareholder may receive fewer shares or more shares than originally owned, depending on that day’s NAVs. Please contact your tax adviser regarding the tax consequences of any conversion.

General.    State Street will not issue share certificates unless you request them. The Fund reserves the right to (i) reject any purchase order if, in the opinion of the Fund’s management, it is in the Fund’s best interest to do so, (ii) suspend the offering of shares for any period of time, and (iii) waive the Fund’s minimum purchase requirements. The Fund also offers another class of shares under different selling and shareholder servicing arrangements pursuant to a separate Prospectus. Except for differences attributable to these arrangements, the shares of all classes are substantially the same.

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Customer Identification Program.    Federal law requires the Fund to obtain, verify, and record identifying information, which may include the name, residential or business address, date of birth (for an individual), social security or taxpayer identification number, or other identifying information, for each investor who opens or reopens an account with the Fund. Applications without the required information may be rejected or placed on hold until the Fund verifies the account holder’s identity.

Third Party Arrangements.    In addition to, or in lieu of amounts received by broker-dealers or other financial intermediaries as reallowances of a portion of sales commissions, the Adviser and its affiliates utilize a portion of their assets, which may include revenues received under the Plans, to pay all or a portion of the charges of various programs that make shares of the Fund available to their customers. These payments, sometimes referred to as “revenue sharing,” do not change the price paid by investors to purchase the Fund’s shares or the amount the Fund receives as proceeds from such sales. Revenue sharing payments may be made to broker-dealers and other financial intermediaries that provide services to the Fund or to shareholders in the Fund, including (without limitation) the following programs: shareholder servicing to Fund shareholders, transaction processing, subaccounting services, marketing support, access to sales meetings, sales representatives and management representatives of the broker-dealers or other financial intermediaries. Revenue sharing payments may also be made to broker-dealers and other financial intermediaries for inclusion of the Fund on a sales list, including a preferred or select sales list, and in other sales programs. These payments may take a variety of forms, including (without limitation) compensation for sales, “trail” fees for shareholder servicing and maintenance of shareholder accounts, and finders’ fees that vary depending on the share class and the dollar amount of shares sold. Revenue sharing payments may be structured: (i) as a percentage of sales; (ii) as a percentage of net assets; and/or (iii) as a fixed dollar amount.

The Adviser may also provide non-cash compensation to broker-dealers, firms, or other financial intermediaries, in accordance with applicable rules of the Financial Industry Regulatory Authority, Inc. (“FINRA”), such as the reimbursement of travel, lodging, and meal expenses incurred in connection with attendance at educational and due diligence meetings or seminars by qualified registered representatives of those firms and, in certain cases, their families; meeting fees; certain entertainment; reimbursement for advertising or other promotional expenses; or other permitted expenses as determined in accordance with applicable FINRA rules. In certain cases these other payments could be significant.

Subject to tax limitations and approval by the Board, the Fund may also make payments to third parties out of its own assets (other than Rule 12b-1 payments) for a portion of the charges for those programs that generally represent savings of expenses experienced by the Fund resulting from shareholders investing in the Fund through such programs rather than investing directly in the Fund.

The Adviser negotiates the level of payments described above to any particular broker-dealer, or financial intermediary with each firm. Currently, such payments (expressed as a percentage of net assets) range from 0.10% to 0.40% per year of the average daily net assets of the Fund attributable to the particular firm depending on the nature and level of services and other factors. In the case of Class I Shares, the Fund may not make any payments for distribution related services.

In addition, in certain cases, broker-dealers or other financial intermediaries, may have agreements pursuant to which shares of the Fund owned by their clients are held of record on the books of the Fund in omnibus accounts maintained by each intermediary, and the intermediaries provide those Fund shareholders with sub-administration and sub-transfer agency services. Pursuant to the Fund’s transfer

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agency agreement, the Fund pays the transfer agent a fee for each shareholder account. As a result, the use of one omnibus account for multiple beneficial shareholders can create a cost savings to the Fund. The Board of Directors may, from time to time, authorize the Fund to pay a portion of the fees charged by these intermediaries if (i) a cost savings to the Fund can be demonstrated and (ii) the omnibus account of the intermediary has net assets in the Fund in excess of $10 million. In these cases, the Board may authorize the Fund to pay a portion of the fees to the intermediary in an amount no greater than the lower of the transfer agency cost savings relating to the particular omnibus account or 0.10% of the average daily net assets of that omnibus account. These payments compensate these intermediaries for the provision of sub-administration and sub-transfer agency services associated with their clients whose shares are held of record in this manner.

Additional Purchase Information for Class A Shares, Class C Shares, and Class I Shares

Retirement Plans/Education Savings Plans.    The Fund makes available IRAs and “Coverdell” Education Savings Plans for investment in Fund shares. Applications may be obtained from the Distributor by calling 800-GABELLI (800-422-3554). Self-employed investors may purchase shares of the Fund through tax-deductible contributions to existing retirement plans for self-employed persons, known as “Keogh” or “H.R.-10” plans. The Fund does not currently act as a sponsor to such plans. Fund shares may also be a suitable investment for other types of qualified pension or profit-sharing plans which are employer sponsored, including deferred compensation or salary reduction plans known as “401(k) Plans.” The minimum initial investment in all such retirement and education savings plans is $250. There is no minimum subsequent investment for retirement or education savings plans.

Automatic Investment Plan.    The Fund offers an automatic monthly investment plan. There is no minimum initial investment for accounts establishing an automatic investment plan. Call your financial intermediary or the Distributor at 800-GABELLI (800-422-3554) for more details about the plan.

Telephone or Internet Investment Plan.    You may purchase additional shares of the Fund by telephone and/or over the Internet if your bank is a member of the ACH system. You must also have a completed and approved Account Options Form on file with the Transfer Agent. There is a minimum of $100 for each telephone or Internet investment. However, you may split the $100 minimum between two funds. To initiate an ACH purchase, please call 800-GABELLI (800-422-3554) or 800-872-5365, or visit our website at www.gabelli.com.

REDEMPTION OF SHARES

You can redeem shares of the Fund on any Business Day. The Fund may temporarily stop redeeming its shares when the NYSE is closed or trading on the NYSE is restricted, when an emergency exists and the Fund cannot sell its shares or accurately determine the value of its assets, or if the SEC orders the Fund to suspend redemptions.

The Fund redeems its shares based on the NAV next determined after the time as of which the Fund receives your redemption request in proper form, subject in some cases to a CDSC, as described under “Classes of Shares — Contingent Deferred Sales Charges” or a redemption fee as described. See “Pricing of Fund Shares” herein for a description of the calculation of NAV.

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You may redeem shares through a broker-dealer or other financial intermediary that has entered into a selling agreement with the Distributor. The broker-dealer or other financial intermediary will transmit a redemption order to State Street on your behalf. The redemption request will be effected at the NAV next determined (less any applicable CDSC) after the Fund receives the request in proper form. If you hold share certificates, you must present the certificates endorsed for transfer.

The Fund is intended for long term investors and not for those who wish to trade frequently in Fund shares. The Fund believes that excessive short term trading of Fund shares creates risks for the Fund and its long term shareholders, including interference with efficient portfolio management, increased administrative and brokerage costs, and potential dilution in the value of Fund shares.

In addition, because the Fund may invest in foreign securities traded primarily on markets that close prior to the time the Fund determines its NAV, frequent trading by some shareholders may, in certain circumstances, dilute the value of Fund shares held by other shareholders. This may occur when an event that affects the value of the foreign securities takes place after the close of the primary foreign market, but before the time that the Fund determines its NAV. Certain investors may seek to take advantage of the fact that there will be a delay in the adjustment of the market price for a security caused by this event until the foreign market reopens (referred to as price arbitrage). If this occurs, frequent traders who attempt this type of price arbitrage may dilute the value of the Fund’s shares to the extent they receive shares or proceeds based upon NAVs that have been calculated using the closing market prices for foreign securities, if those prices have not been adjusted to reflect a change in the fair value of the foreign securities. In an effort to prevent price arbitrage, the Fund has procedures designed to adjust closing market prices of foreign securities before it calculates its NAV when it believes such an event has occurred that will have more than the minimal effect on the NAV. Prices are adjusted to reflect what the Fund believes are the fair values of these foreign securities at the time the Fund determines its NAV (called fair value pricing). Fair value pricing, however, involves judgments that are inherently subjective and inexact since it is not always possible to be sure when an event will affect a market price and to what extent. As a result, there can be no assurance that fair value pricing will always eliminate the risk of price arbitrage.

In order to discourage frequent short term trading in Fund shares, the Fund has adopted policies and procedures which impose a 2.00% redemption fee (short term trading fee) on Class A, Class C, and Class I Shares that are redeemed or exchanged within seven days of a purchase. This fee is calculated based on the shares’ aggregate NAV on the date of redemption and deducted from the redemption proceeds. The redemption fee is not a sales charge; it is retained by the Fund and does not benefit the Fund’s Adviser or any other third party. For purposes of computing the redemption fee, shares will be redeemed in reverse order of purchase (the latest shares acquired will be treated as being redeemed first). Redemptions to which the fee applies include redemption of shares resulting from an exchange made pursuant to the Fund’s exchange privilege. The redemption fee will not apply to redemptions of shares where (i) the shares were purchased through automatic reinvestment of dividends or other distributions, (ii) the redemption is initiated by the Fund, (iii) the shares were purchased through programs that collect the redemption fees at the program level and remit them to the Fund, or (iv) the shares were purchased through programs that the Adviser determines to have appropriate anti-short term trading policies in place or as to which the Adviser has received assurances that look through redemption fee procedures or effective anti-short term trading policies and procedures are in place.

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While the Fund has entered into information sharing agreements with financial intermediaries which contractually require such financial intermediaries to provide the Fund with information relating to their customers investing in the Fund through non-disclosed or omnibus accounts, the Fund cannot guarantee the accuracy of the information provided to it from financial intermediaries and may not always be able to track short term trading effected through these financial intermediaries. In addition, because the Fund is required to rely on information provided by the financial intermediary as to the applicable redemption fee, the Fund cannot guarantee that the financial intermediary is always imposing such fee on the underlying shareholder in accordance with the Fund’s policies. Subject to the exclusions discussed above, the Fund seeks to apply these policies uniformly.

Certain financial intermediaries may have procedures which differ from those of the Fund to collect the redemption fees or that prevent or restrict frequent trading. Investors should refer to their intermediary’s policies on frequent trading restrictions.

The Fund continues to reserve all rights, including the right to refuse any purchase request (including requests to purchase by exchange) from any person or group who, in the Fund’s view, is likely to engage in excessive trading or if such purchase is not in the best interest of the Fund and to limit, delay, or impose other conditions on exchanges or purchases. The Fund has adopted a policy of seeking to minimize short term trading in its shares and monitors purchase and redemption activities to assist in minimizing short term trading.

In the event that you wish to redeem shares in a registered account established by a broker-dealer or other financial intermediary and you are unable to contact your broker-dealer or financial intermediary, you may redeem shares by mail. You may mail a letter requesting the redemption of shares to: The Gabelli Funds, P.O. Box 8308, Boston, MA 02266-8308. Your letter should state the name of the fund(s) and the share class, the dollar amount or number of shares you wish to redeem, and your account number. You must sign the letter in exactly the same way the account is registered. If there is more than one owner of shares, all owners must sign. A medallion signature guarantee is required for each signature on your redemption letter. You can obtain a medallion signature guarantee from financial institutions such as commercial banks, broker-dealers, and savings banks and credit unions. A notary public cannot provide a medallion signature guarantee.

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Automatic Cash Withdrawal Plan. You may automatically redeem shares on a monthly, quarterly or annual basis if you have at least $10,000 in your account and if your account is directly registered with State Street. Call 800-GABELLI (800-422-3554) for more information about this plan.

Involuntary Redemption. The Fund may redeem all shares in your account (other than an IRA) if the value falls below $1,000 as a result of redemptions (but not as a result of a decline in NAV). You will be notified in writing before the Fund initiates such action and you will be allowed thirty days to increase the value of your account to at least $1,000.

Reinstatement Privilege. A shareholder in the Fund who has redeemed Class A Shares may reinvest, without a sales charge, up to the full amount of such redemption at the NAV determined at the time of the reinvestment within forty-five days of the original redemption. A redemption is a taxable transaction and a gain or loss may be recognized for federal income tax purposes even if the reinstatement privilege is exercised. However, any loss realized upon the redemption will not be recognized as to the number of shares acquired by reinstatement, except through an adjustment in the tax basis of the shares so acquired if those shares are acquired within thirty days of the redemption.

Redemption Proceeds. A redemption request received by the Fund will be effected based on the NAV next determined after the time as of which the Fund, or if applicable, its authorized designee, receives the request. If you request redemption proceeds by check, the Fund will normally mail the check to you within seven days after receipt of your redemption request. If you purchased your Fund shares by check or through the Automatic Investment Plan, you may not receive proceeds from your redemption until the check clears, which may take up to as many as ten days following the purchase. While the Fund will delay the processing of the redemption payment until the check clears, your shares will be valued at the next determined NAV after receipt of your redemption request.

Redemption in Kind. In certain circumstances, the Fund may pay your redemption proceeds wholly or partially in portfolio securities. Where applicable, payments would be made in Portfolio securities only in the rare instance that the Fund’s Board believes that it would be in the best interest not to pay redemption proceeds in cash. A redemption in kind would be a taxable event to you on which you would realize capital gain or capital loss (subject to possible limitations of deductibility).

EXCHANGE OF SHARES

You can exchange shares of the Fund for shares of the same class of other funds managed by the Adviser or its affiliates based on their relative NAVs at the time of exchange. You may call your broker to

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obtain a list of the funds whose shares you may acquire through an exchange. Class C Shares will continue to age from the date of the original purchase of such shares and will assume the CDSC rate such shares had at the time of exchange. You may also exchange your shares for shares of the same class of a money market fund managed by the Adviser or its affiliates, without imposition of any CDSC at the time of exchange. Upon subsequent redemption from such money market fund or the Fund (after re-exchange into the Fund), such shares will be subject to the CDSC calculated by excluding the time such shares were held in a Gabelli money market fund. The Fund may impose limitations on, or terminate, the exchange privilege with respect to any investor at any time. You will be given notice at least sixty days prior to any material change in the exchange privilege. An exchange of shares is a taxable event to you on which you would realize capital gain or capital loss (subject to possible limitations of deductibility).

In effecting an exchange:

You may exchange shares through the Distributor, directly from the Transfer Agent, or through a financial intermediary that has entered into the appropriate selling agreement with the Distributor.

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Your financial intermediary may charge you a processing fee for assisting you in purchasing or redeeming shares of the Fund. This charge is set by your financial intermediary and does not benefit the Fund, the Distributor, or the Adviser in any way. It would be in addition to the sales charges and other costs, if any, described in this Prospectus and must be disclosed to you by your financial intermediary.

PRICING OF FUND SHARES

The NAV is calculated separately for each class of shares on each Business Day. The NYSE is open Monday through Friday, but currently is scheduled to be closed on New Year’s Day, Martin Luther King, Jr. Day, Presidents’ Day, Good Friday, Memorial Day, Independence Day, Labor Day, Thanksgiving Day, and Christmas Day and on the preceding Friday or subsequent Monday when a holiday falls on a Saturday or Sunday, respectively.

The Fund’s NAV is determined as of the close of regular trading on the NYSE, normally 4:00 p.m., Eastern Time. The NAV of each class is computed by dividing the value of the Fund’s net assets, i.e., the value of its securities and other assets less its liabilities, including expenses payable or accrued but excluding capital stock and surplus, attributable to the applicable class of shares by the total number of shares of such class outstanding at the time the determination is made. The price of Fund shares for the purpose of purchase and redemption orders will be based upon the calculation of the NAV of each class next made after the time as of which the purchase or redemption order is received in proper form. Because the Fund may invest in foreign securities that are primarily listed on foreign exchanges that trade on weekends or other days when the Fund does not price its shares, the NAV of the Fund’s shares may change on days when shareholders will not be able to purchase or redeem the Fund’s shares.

Portfolio securities listed or traded on a nationally recognized securities exchange or traded in the U.S. over-the-counter market for which market quotations are readily available are valued at the last quoted sale price or a market’s official closing price as of the close of business on the day the securities are being valued. If there were no sales that day, the security is valued at the average of the closing bid and asked prices or, if there were no asked prices quoted on that day, then the security is valued at the closing bid price on that day. If no bid or asked prices are quoted on such day, the security is valued at the most recently available price or, if the Board so determines, by such other method as the Board shall determine in good faith to reflect its fair market value. Portfolio securities traded on more than one national securities exchange or market are valued according to the broadest and most representative market, as determined by the Adviser.

Portfolio securities primarily traded on a foreign market are generally valued at the preceding closing values of such securities on the relevant market, but may be fair valued pursuant to procedures established by the Board if market conditions change significantly after the close of the foreign market but prior to the close of business on the day the securities are being valued. Debt instruments with remaining maturities of sixty days or less that are not credit impaired are valued at amortized cost, unless the Board determines such amount does not reflect the securities’ fair value, in which case these securities will be fair valued as determined by the Board. Debt instruments having a maturity greater than sixty days for which market quotations are readily available are valued at the average of the latest bid and asked prices. If there were no asked prices quoted on such day, the security is valued using the closing bid price. U.S. government obligations with maturities greater than sixty days are normally valued using a model that incorporates market observable data such as reported sales of similar securities, broker quotes, yields,

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bids, offers, and reference data. Certain securities are valued principally using dealer quotations. Futures contracts are valued at the closing settlement price of the exchange or board of trade on which the applicable contract is traded.

Securities and other assets for which market quotations are not readily available are fair valued as determined by the Board. Fair valuation methodologies and procedures may include, but are not limited to: analysis and review of available financial and non-financial information about the company; comparisons with the valuation and changes in valuation of similar securities, including a comparison of foreign securities with the equivalent U.S. dollar value American Depositary Receipt securities at the close of the U.S. exchange; and evaluation of any other information that could be indicative of the value of the security.

DIVIDENDS AND DISTRIBUTIONS

The Fund intends to pay dividends and capital gain distributions, if any, on an annual basis. You may have dividends and/or capital gain distributions that are declared by the Fund reinvested automatically at NAV in additional shares of the Fund. You will make an election to receive dividends and distributions in cash or Fund shares at the time you first purchase your shares. You may change this election by notifying the Fund or your financial intermediary in writing at any time prior to the record date for a particular dividend or distribution. There are no sales or other charges by the Fund in connection with the reinvestment of dividends and capital gain distributions. Shares purchased through dividend reinvestment will receive a price without sales charge based on the NAV on the reinvestment date, which is typically the date dividends are paid to shareholders. There is no fixed dividend rate, and there can be no assurance that the Fund will realize any capital gains or other income with which to pay dividends and distributions. Distributions are taxable to you whether received in cash or additional shares. A dividend or capital gain distribution paid on shares purchased shortly before the record date for that dividend or distribution was declared will be subject to income taxes. Dividends and distributions may be different for different classes of shares of the Fund.

TAX INFORMATION

The Fund expects that distributions will consist primarily of investment company taxable income and net capital gain. Capital gains may be taxed at different rates depending on the length of time the Fund holds the securities giving rise to such capital gains. Dividends out of investment company taxable income (including distributions of net short term capital gains, i.e., gains from securities held by the Fund for one year or less) are taxable to you as ordinary income, except, as discussed below, that qualified dividends of individual taxpayers may be eligible for a reduced federal income tax rate. Properly reported distributions of net capital gain, i.e., net long term capital gains minus net short term capital loss (“Capital Gains Distributions”) are taxable to you at long term capital gain rates no matter how long you have owned your shares. The Fund’s dividends and distributions, whether you receive them in cash or reinvest them in additional shares of the Fund, generally will be subject to federal and, if applicable, state and local taxes. Although dividends (including dividends from short term capital gains) are generally taxable as ordinary income, individual shareholders who satisfy certain holding periods and other requirements are taxed on such dividends at long term capital gain rates to the extent the dividends are attributable to “qualified dividend income” received by the Fund. Qualified dividend income generally consists of

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dividends received from U.S. corporations (other than dividends from tax-exempt organizations and certain dividends from real estate investment trusts and regulated investment companies) and certain foreign corporations (generally those eligible for the benefits of a tax treaty with the United States and those whose stock is traded on an established securities market in the United States). The amount of qualified dividend income distributed by the Fund in any year depends on its investments and cannot be predicted. Corporations may be able to take a dividends received deduction for a portion of the income dividends they receive. A redemption of Fund shares or an exchange of Fund shares for shares of another fund will be treated for tax purposes as a sale of Fund shares, and any gain you realize on such a transaction generally will be taxable.

The Fund may be required to withhold as backup withholding, currently at a rate of 28%, a portion of the dividends, distributions, and redemption proceeds payable to shareholders who fail to provide the Fund with their correct taxpayer identification number or to make required certifications, or who have been notified by the Internal Revenue Service (“IRS”) that they are subject to backup withholding. Additionally, the Fund will withhold when the IRS notifies the Fund that backup withholding is required. Also, dividends, distributions, and redemption proceeds payable to foreign shareholders may be subject to a federal withholding tax.

Dividends declared by the Fund in October, November, or December to shareholders of record on a specified date in such a month and paid in January of the following year will be treated as paid in December for tax purposes.

The Fund may be subject to foreign withholding and other taxes. The Fund expects to be eligible to elect for U.S. federal income tax purposes to treat any foreign income taxes paid by it as paid by its shareholders. If the Fund makes the election, the amount of foreign income taxes paid by the Fund would be included in the income of its shareholders and the shareholders may elect, subject to certain limitations, to credit such amount included against their U.S. tax due, if any, or to deduct such amount from their U.S. taxable income, if any.

After the end of each year, the Fund will provide you with information regarding any shares you redeemed and the federal tax status of any dividends or distributions you received during the previous year.

If you sell your Fund’s shares, it is considered a taxable event for you. Depending on the purchase price and the sale price of the shares you sell, you may have a gain or a loss on the transaction. You are responsible for any tax liabilities generated by your transaction.

Dividends and net capital gains are generally subject to a 3.8% federal tax on net investment income for shareholders whose adjusted gross income exceeds $200,000 for single filers and $250,000 for married joint filers.

This summary of tax consequences is intended for general information only and is subject to change by legislative, judicial, or administrative action, and any such change may be retroactive. It is applicable only to shareholders who are U.S. persons. The Fund may make taxable distributions during periods in which the share price has declined. A more complete discussion of the tax rules applicable to you and the Fund can be found in the SAI that is incorporated by reference into this Prospectus. You should consult a tax adviser concerning the tax consequences of your investment in the Fund.

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MAILINGS AND E-DELIVERY TO SHAREHOLDERS

In our continuing effort to reduce duplicative mail and Fund expenses, we currently send a single copy of prospectuses and shareholder reports to your household even if more than one member in your household owns the same fund or funds described in the prospectus or report. Additional copies of our prospectuses and reports may be obtained by calling 800-GABELLI (800-422-3554). If you do not want us to continue to consolidate your fund mailings and would prefer to receive separate mailings at any time in the future, please call us at the telephone number above and we shall resume separate mailings, in accordance with your instructions, within thirty days of your request. The Fund offers electronic delivery of Fund documents. Direct shareholders of the Fund can elect to receive the Fund’s annual, semiannual, and quarterly reports, as well as manager commentaries and prospectuses via e-delivery. For more information or to sign up for e-delivery, please visit the Fund’s website at www.gabelli.com. Shareholders who purchase shares of the Fund through a financial intermediary should contact their financial intermediary to sign up for e-delivery of Fund documents, if available.

FINANCIAL HIGHLIGHTS

The Financial Highlights table is intended to help you understand the financial performance of the Fund for the past five fiscal years. The total returns in the table represent the percentage amount that an investor would have earned or lost on an investment in the designated Class of Shares (assuming reinvestment of all distributions). This information has been audited by Ernst & Young LLP, independent registered public accounting firm, whose report, along with the Fund’s financial statements and related notes, is included in the Fund’s annual report, which is available upon request.

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GAMCO International Growth Fund, Inc.

Financial Highlights

Selected data for a share of capital stock outstanding throughout each year:

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GAMCO International Growth Fund, Inc.

Class A, C, and I Shares

For More Information:

For more information about the Fund, the following documents are available free upon request:

Annual/Semiannual Reports:

The Fund’s semiannual and audited annual reports to shareholders contain additional information on the Fund’s investments. In the Fund’s annual report, you will find a discussion of the market conditions and investment strategies that significantly affected the Fund’s performance during its last fiscal year.

Statement of Additional Information (SAI):

The SAI provides more detailed information about the Fund, including its operations and investment policies. It is incorporated by reference, and is legally considered a part of this Prospectus.

You can obtain free copies of these documents and prospectuses of other funds in the Gabelli/GAMCO family, or request other information and discuss your questions about the Fund by mail, toll free telephone, or the internet as follows:

The GAMCO International Growth Fund, Inc.

One Corporate Center

Rye, NY 10580-1422

Telephone: 800-GABELLI (800-422-3554)

www.gabelli.com

You can also review and/or copy the Fund’s Prospectuses, annual and semiannual reports, and SAI at the Public Reference Room of the SEC in Washington, DC. You can obtain text-only copies:

(Investment Company Act File No. 811-08560)