The GAMCO Growth Fund

SUMMARY PROSPECTUS April 30, 2014

Class AAA (GABGX)

Before you invest, you may want to review the Fund’s Prospectus and Statement of Additional Information (“SAI”), which contain more information about the Fund and its risks. You can find the Fund’s Prospectus and SAI and other information about the Fund online at www.gabelli.com. You can also get this information at no cost by calling 800-422-3554 or by sending an email request to info@gabelli.com. The Fund’s Prospectus and SAI, both dated April 30, 2014, are incorporated by reference into this Summary Prospectus.

Investment Objective

The GAMCO Growth Fund (the “Fund”) primarily seeks to provide capital appreciation. The Fund’s secondary goal is to produce current income.

Fees and Expenses of the Fund:

This table describes the fees and expenses that you may pay if you buy and hold Class AAA Shares of the Fund.

Expense Example

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

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 that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

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 the Fund’s 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 35% of the average value of its portfolio.

Principal Investment Strategies

The Fund will primarily invest in common stocks. The Fund may also invest in foreign securities. The Fund focuses on securities of companies which appear to have favorable, yet undervalued, prospects for earnings growth and price appreciation. The Fund’s investment adviser, Gabelli Funds, LLC (the “Adviser”), invests the Fund’s assets in companies which the portfolio manager believes have above average or expanding market shares, profit margins, and returns on equity. The Adviser will sell any Fund investments that lose their perceived value when compared with other investment alternatives in the judgment of the portfolio manager.

The Adviser uses fundamental security analysis to develop earnings forecasts for companies and to identify investment opportunities. The Adviser bases its analysis on general economic and industry data provided by the U.S. Government, various trade associations and other sources, and published corporate financial data such as annual reports, 10-Ks, and quarterly statements as well as direct interviews with company management. Generally, the Adviser makes investment decisions first by looking at individual companies and then by scrutinizing their growth prospects in relation to their industries and the overall economy. The Adviser seeks to invest in companies with high future earnings potential relative to their current market valuations. The Fund may invest up to 25% of its total assets in securities of non-U.S. issuers.

The Fund’s assets will be invested primarily in a broad range of readily marketable equity securities consisting of common stock and preferred stock. Many of these common stocks will not pay dividends; instead, stocks will be bought for the potential that their prices will increase, providing capital appreciation for the Fund. The value of equity securities will fluctuate due to many factors, including the past and predicted earnings of the issuer, the quality of the issuer’s management, general market conditions, the forecasts for the issuer’s industry, and the value of the issuer’s assets. Holders of equity securities only have rights to value in the company after all issuer debts have been paid, and they could lose their entire investment in a company that encounters financial difficulty. The Fund may also buy warrants which are rights to purchase securities at a specified time at a specified price. For additional information about selection of investments suitable for the Fund, see page 7 of the Prospectus.

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. Stocks are subject to market, economic, and business risks that may cause their prices to fluctuate. When you sell Fund shares, they may be worth less than what you paid for them. Consequently, you can lose money by investing in the Fund. Foreign securities are subject to currency, information, and political risks. The Fund is also subject to the risk that the portfolio manager’s judgments about the above average growth potential of particular companies’ stocks is incorrect and the perceived value of such stocks is not realized by the market, or their prices decline.

Investing in the Fund involves the following risks:

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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 annual returns for one year, five years, and ten years compared with those of broad based securities market indices. 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.

THE GAMCO GROWTH FUND (Total Returns for the Years Ended December 31)

During the years shown in the bar chart, the highest return for a quarter was 20.39% (quarter ended June 30, 2009) and the lowest return for a quarter was (27.53)% (quarter ended December 31, 2008).

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. 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”).

Management

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

The Portfolio Manager. Mr. Howard F. Ward, CFA, Portfolio Manager of the Adviser and Chief Investment Officer of Growth Products for GAMCO Investors, Inc., has served as Portfolio Manager of the Fund since 1995.

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Purchase and Sale of Fund Shares

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

You can purchase or redeem shares of the Fund 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 (“G.distributors” or the “Distributor”), an affiliate of the Adviser. 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.

Tax Information

The Fund expects that distributions will generally be taxable as ordinary income or long term capital gains 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 shares of 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.

406 2014

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