MainStay Equity Index Fund		Summary Prospectus February 28, 2012
Class/Ticker	A MCSEX

Before you invest, you may want to review the Fund's Prospectus, which contains more information about the Fund and its risks. You can find the Fund's Prospectus and other information about the Fund by going online to mainstayinvestments.com/documents, by calling 800-MAINSTAY (624-6782) or by sending an e-mail to MainStayShareholderServices@nylim.com. The Fund's Prospectus and Statement of Additional Information, both dated February 28, 2012, are incorporated by reference into this Summary Prospectus.

Investment Objective

The Fund seeks investment results that correspond to the total return performance (reflecting reinvestment of dividends) of publicly traded common stocks represented by the S&P 500^® Index.

The Fund is closed to new investors and new share purchases. No purchase orders, systematic investments or exchanges are being accepted. Existing shareholders are permitted to reinvest dividends and capital gains only.

The Board of Trustees of the Fund recently approved a proposal to reorganize the Fund into MainStay S&P 500 Index Fund, a series of MainStay Funds Trust with substantially the same investment objective as the Fund. Proxy materials describing the proposed reorganization will be mailed to the Fund’s record date shareholders. If shareholders of the Fund approve the reorganization, it is expected to be completed in the second quarter of 2012. For additional information regarding the investment strategies and principal risks of MainStay S&P 500 Index Fund, please see that Fund’s prospectus, which can be located at mainstayinvestments.com.

Fees and Expenses of the Fund

The table below describes the fees and expenses that you may pay if you hold shares of the Fund. The Fund is closed to new investors and new share purchases.

	Class A
Shareholder Fees (fees paid directly from your investment)
Maximum Sales Charge (Load) imposed on Purchases (as a percentage of offering price)	3.00	%
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of the original offering price or redemption proceeds)	None
Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Management Fees (as an annual percentage of the Fund's average daily net assets)1	0.27	%
Distribution and/or Service (12b-1) Fees	0.25	%
Other Expenses	0.29	%
Total Annual Fund Operating Expenses)2	0.81	%
Waivers / Reimbursements)2	(0.21	)%
Total Annual Fund Operating Expenses After Waivers / Reimbursements)2	0.60	%

1.The management fee is as follows: 0.25% on assets up to $1 billion; 0.225% on assets from $1 billion up to $3 billion; and 0.20% on assets in excess of $3 billion, plus a fee for fund accounting services previously provided by New York Life Investment Management LLC ("New York Life Investments") under a separate fund accounting agreement. This addition to the management fee amounted to 0.02% of the Fund's average daily net assets, but did not result in a net increase in the Fund’s Total Annual Fund Operating Expenses. New York Life Investments has contractually agreed to waive its management fee to 0.19% on assets up to $1 billion; 0.165% on assets from $1 billion up to $3 billion; and 0.14% on assets in excess of $3 billion. This agreement will remain in effect until February 28, 2013, and shall renew automatically for one-year terms unless New York Life Investments provides written notice of termination prior to the start of the next term or upon approval of the Board of Trustees of the Fund.

2.New York Life Investments has contractually agreed to waive fees and/or reimburse expenses so that Total Annual Fund Operating Expenses (excluding taxes, interest, litigation, extraordinary expenses, brokerage and other transaction expenses relating to the purchase or sale of portfolio investments, and acquired (underlying) fund fees and expenses) for Class A shares do not exceed 0.60% of the Fund’s average daily net assets. This agreement will remain in effect until February 28, 2013, and shall renew automatically for one-year terms unless New York Life Investments provides written notice of termination prior to the start of the next term or upon approval of the Board of Trustees of the Fund.

Example

The Example is intended to help you compare the cost of investing in 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:

(NYLIM) NL003 MSEI01-02/12

Expenses After	Class A
1 Year	$      359
3 Years	$      530
5 Years	$      716
10 Years	$   1,253

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 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 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 4% of the average value of its portfolio.

Principal Investment Strategies

The Fund normally invests at least 80% of its assets (net assets plus any borrowings for investment purposes) in stocks as represented in the Standard & Poor's 500^® ("S&P 500^®") Index, and in the same proportion, to the extent feasible.

Investment Process: Madison Square Investors LLC, the Fund's Subadvisor, uses statistical techniques to determine which stocks are to be purchased or sold to replicate the S&P 500^® Index to the extent feasible. From time to time, adjustments may be made in the Fund's portfolio because of changes in the composition of the S&P 500^® Index. The correlation between the performance of the Fund and the S&P 500^® Index is expected to be at least 0.95, before charges, fees and expenses, on an annual basis. A correlation of 1.00 would indicate perfect correlation, which would be achieved when the net asset value ("NAV") of the Fund, including the value of its dividend and capital gains distributions, increases or decreases in exact proportion to changes in the S&P 500^® Index.

The Fund's investments also include S&P 500^® Index futures which may be used for cash management purposes.

Guarantee

When issued, shares of the Fund had been subject to an unconditional one-day guarantee from NYLIFE LLC ("NYLIFE"). If, on the business day immediately after ten years from your date(s) of purchase(s) (the "Guarantee Date"), the NAV of a Fund share, plus the value of all cumulative reinvested dividends and distributions attributable to such share paid during that ten-year period ("Guaranteed Share"), was less than the price initially paid for the Guaranteed Share, NYLIFE would pay each holder of a Guaranteed Share an amount equal to the difference between the Guaranteed Amount for each such share and the NAV of such Guaranteed Share outstanding and held by the shareholder as of the close of business on the Guarantee Date. See "The MainStay Equity Index Fund Guarantee" on page 7 of the Prospectus.

The Fund was closed to both new investors and new share purchases on January 2, 2002, and as such, as of the date of this Prospectus, it is anticipated that NYLIFE will have fulfilled its obligations to shareholders pursuant to the terms of the Guarantee. NYLIFE will continue to process payments subject to the Guarantee, if applicable.

Principal Risks

Loss of Money Risk: Before considering an investment in the Fund, you should understand that you could lose money.

Market Changes Risk:The value of the Fund's investments may change because of broad changes in the markets in which the Fund invests, which could cause the Fund to underperform other funds with similar objectives.

Management Risk: The investment strategies, practices and risk analysis used by the Fund's Subadvisor may not produce the desired results.

Equity Securities Risk: Investments in common stocks and other equity securities are particularly subject to the risk of changing economic, stock market, industry and company conditions and the risks inherent in the portfolio manager's ability to anticipate such changes that can adversely affect the value of the Fund's holdings. Opportunity for greater gain often comes with greater risk of loss.

S&P 500^® Index Risk: If the value of the S&P 500^® Index declines, the net asset value of shares of the Fund will also decline. The Fund's ability to mirror the S&P 500^® Index may be affected by, among other things, transaction costs; changes in either the composition of the S&P 500^® Index or the number of shares outstanding for the components of the S&P 500^® Index; and the timing and amount of contributions to, and redemptions from, the Fund by shareholders.

Derivatives Risk: Derivatives are investments whose value depends on (or is derived from) the value of an underlying instrument, such as a security, asset, reference rate or index. Derivative strategies often involve leverage, which may exaggerate a loss, potentially causing the Fund to lose more money than it would have lost had it invested in the underlying instrument. Derivatives may be difficult to sell, unwind or value. Derivatives may also be subject to counterparty risk, which is the risk that the counterparty (the party on the other side of the transaction) on a derivative transaction will be unable to honor its contractual obligations to the Fund. Futures may be more volatile than direct investments in the instrument underlying the futures, and may not correlate perfectly to the underlying instrument. Futures also may involve a small initial investment relative to the risk assumed, which could result in losses greater than if they had not been used.

Past Performance

The following bar chart and tables indicate some of the risks of investing in the Fund. The bar chart shows you how the Fund's calendar year performance has varied over the last ten years. Sales loads are not reflected in the bar chart. If they were, returns would be less than those shown. The average annual

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total returns table shows how the Fund's average annual total returns (before and after taxes) for the one-, five- and ten-year periods compare to those of a broad-based securities market index. The Fund has selected the S&P 500^® Indexas its primary benchmark. The S&P 500^® Index is widely regarded as the standard index for measuring large-cap U.S. stock market performance.

Class A shares were first offered on December 20, 1990. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Please visit mainstayinvestments.com for more recent performance information.

Annual Returns, Class A Shares

(by calendar year 2002-2011)

Best Quarter
2Q/09	15.90	%
Worst Quarter
4Q/08	-22.10	%

Average Annual Total Returns (for the periods ended December 31, 2011)

	1 Year		5 Years		10 Years
Return Before Taxes
Class A	-1.49	%	-1.34	%	1.98	%
Return After Taxes on Distributions
Class A	-1.70	%	-1.59	%	1.66	%
Return After Taxes on Distributions and Sale of Fund Shares
Class A	-0.68	%	-1.16	%	1.61	%
S&P 500® Index (reflects no deductions for fees, expenses, or taxes)	2.11	%	-0.25	%	2.92	%

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 cases, the return after taxes may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of shares at the end of the measurement period. Actual after-tax returns depend on your tax situation and may differ from those shown. After-tax returns are not relevant if you hold your shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns shown are for Class A shares.

Management

New York Life Investments serves as the Fund's Manager. Madison Square Investors LLC serves as the Fund's Subadvisor.

Subadvisor	Portfolio Manager	Service Date
Madison Square Investors LLC	Francis J. Ok, Managing Director	Since 1996

How to Sell Shares

The Fund is closed to new investors and new share purchases. You may sell shares of the Fund on any day the Fund is open for business by contacting your financial intermediary or other financial institution, or by contacting the Fund by telephone at 800-MAINSTAY (624-6782), by mail at MainStay Funds, P.O. Box 8401, Boston, MA 02266-8401 or by accessing our website at mainstayinvestments.com.

Tax Information

The Fund's distributions are generally taxable to you as ordinary income, capital gains, or a combination of the two, unless you are investing through a tax-deferred arrangement, such as a 401(k) plan or an individual retirement account.

Compensation to Financial Intermediary Firms

If you purchase Fund shares through a financial intermediary firm (such as a broker/dealer or 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 financial intermediary firm or your financial adviser to recommend the Fund over another investment. Ask your financial adviser or visit your financial intermediary firm's website for more information. For additional information about compensation to financial intermediaries, please see the section entitled "Compensation to Financial Intermediary Firms" in the "Shareholder Guide" section starting on page 10 of the Prospectus.

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