May 30, 2007

DREYFUS BASIC U.S. MORTGAGE SECURITIES FUND 

Supplement to Prospectus

dated May 1, 2007

The following information supplements the information contained in the “Goal/Approach” section of the fund’s Prospectus:

The fund may enter into forward contracts and swap agreements, such as interest rate swaps and credit default swaps. Swap Agreements can be used to transfer the credit risk of a security without actually transferring ownership of the security or to customize exposure to particular credits. The fund also may make forward commitments in which the fund agrees to buy or sell a security in the future at a price agreed upon today.

The following information supplements the information contained in the “Main Risks--Derivatives risk” section of the fund’s Prospectus:

Derivatives risk. In addition to investing in mortgage-related securities, such as CMOs and stripped mortgage-backed securities, the fund may use other derivative instruments, such as options, futures, and options on futures (including those relating to interest rates), forward contracts, swaps (including credit default swaps on mortgage-related and asset-backed securities), options on swaps, and other credit derivatives. Credit default swaps and similar instruments involve greater risks than if the fund had invested in the reference obligation directly, since, in addition to general market risks, they are subject to illiquidity risk, counterparty risk and credit risks.

Additionally, some derivatives the fund uses involve leverage (e.g., an instrument linked to the value of a securities index may return income calculated as a multiple of the price movement of the underlying index). This economic leverage will increase the volatility of these instruments as they may increase or decrease in value more quickly than the underlying security, index, futures contracts, or other economic variable. The fund may be required to segregate permissible liquid assets to cover its obligations relating to its purchase of derivative instruments.

May 30, 2007

DREYFUS BASIC U.S. MORTGAGE SECURITIES FUND 

Supplement to Statement of Additional Information 

Dated May 1, 2007

The following information supplements the information in the section in the Fund’s Statement of Additional Information entitled “Description of the Fund – Investment Techniques - Derivatives”:

Swap Transactions and Other Credit Derivatives. The Fund may engage in swap transactions, including interest rate swaps, interest rate looks, caps, collars and floors, credit default swaps, and index swap agreements and other credit derivative products, to seek to mitigate risk, manage maturity and duration, reduce portfolio turnover, or obtain a particular desired return at a lower cost to the Fund than if the Fund had invested directly in an instrument that yielded the desired return. The Fund also may enter into options on swaps, sometimes called “swaptions.”

     Swap agreements are two party contracts entered into primarily by institutional investors for periods ranging from a few weeks to more than one year. In a standard “swap” transaction, two parties agree to exchange the returns (or differentials in rates of return) earned or realized on particular predetermined investments or instruments. The gross returns to be exchanged or “swapped” between the parties are generally calculated with respect to a “notional amount” i.e., the return on or increase in value of a particular dollar amount invested at a particular interest rate, or in a “basket” of credit default swaps or securities representing a particular index. The “notional amount” of the swap agreement is only used as a basis upon which to calculate the obligations that the parties to a swap agreement have agreed to exchange.

     Most swap agreements entered into by the Fund are cash settled and calculate the obligations of the parties to the agreement on a “net basis.” Thus, the Fund’s current obligations (or rights) under a swap agreement generally will be equal only to the net amount to be paid or received under the agreement based on the relative values of the positions held by each party to the agreement (the “net amount”). The Fund’s current obligations under a swap agreement will be accrued daily (offset against any amounts owed to the Fund) and any accrued but unpaid net amounts owed to a swap counterparty will be covered by the segregation of permissible liquid assets of the Fund.

     A swap option is a contract that gives a counterparty the right (but not the obligation) in return for payment of a premium, to enter into a new swap agreement or to shorten, extend, cancel or otherwise modify an existing swap agreement, at some designated future time on specified terms. A cash-settled option on a swap gives the purchaser the right in return for the premium paid, to receive an amount of cash equal to the value of the underlying swap as of the exercise date. These options typically are purchased in privately negotiated transactions from financial institutions, including securities brokerage firms. Depending on the terms of the particular option agreement, the Fund generally will incur a greater degree of risk when it writes a swap option than it will incur when it purchases a swap option. When the Fund purchases a swap option, it risks losing only the amount of the premium it has paid should it decide to let the option expire unexercised. However, when the Fund writes a swap option, upon exercise of the option the Fund will become obligated according to the terms of the underlying agreement.

     Interest rate swaps are over-the-counter contracts in which each party agrees to make a periodic interest payment based on an index or the value of an asset in return for a periodic payment from the other party based on a different index or asset. The purchase of an interest rate floor entitles the purchaser, to the extent that a specified index falls below a predetermined interest rate, to receive payments of interest on a notional principal amount from the party selling such interest rate floor. The purchase of an interest rate cap entitles the purchaser, to the extent that a specified index rises above a predetermined interest rate, to receive payments of interest on a notional principal amount from the party selling such interest rate cap. Interest rate collars involve selling a cap and purchasing a floor or vice versa to protect the Fund against interest rate movements exceeding given minimum or maximum levels.

     The Fund may enter into credit default swap agreements and similar agreements, which may have as reference obligations securities that are or are not currently held by the Fund. The protection “buyer” in a credit default contract may be obligated to pay the protection “seller” an up front payment or a periodic stream of payments over the term of the contract provided generally that no credit event on a reference obligation has occurred. If a credit event occurs, the seller generally must pay the buyer the “par value” (full notional value) of the swap in exchange for an equal face amount of deliverable obligations of the reference entity described in the swap, or the seller may be required to deliver the related net cash amount, if the swap is cash settled. The Fund may be either the buyer or seller in the transaction. If the Fund is a buyer and no credit event occurs, the Fund recovers nothing if the swap is held through its termination date. However, if a credit event occurs, the Fund may elect to receive the full notional value of the swap in exchange for an equal face amount of deliverable obligations of the reference entity that may have little or no value. As a seller, the Fund generally receives an up front payment or a fixed rate of income throughout the term of the swap, which typically is between six months and three years, provided that there is no credit event. If a credit event occurs, generally the seller must pay the buyer the full notional value of the swap in exchange for an equal face amount of deliverable obligations of the reference entity that may have little or no value. Credit default swaps and similar instruments involve greater risks than if the Fund had invested in the reference obligation directly, since, in addition to general market risks, they are subject to illiquidity risk, counterparty risk and credit risk.

     The Fund may invest in credit linked securities issued by a limited purpose trust or other vehicle that, in turn, invests in a derivative instrument or basket of derivative instruments, such as credit default swaps or interest rate swaps, to obtain exposure to certain fixed income markets or to remain fully invested when more traditional income producing securities are not available. Like an investment in a bond, an investment in these credit linked securities represents the right to receive periodic income payments (in the form of distributions) and payment of principal at the end of the term of the security. However, these payments are conditioned on the issuer’s receipt of payments from, and the issuer’s potential obligations to, the counterparties to certain derivative instruments entered into by the issuer of the credit linked security. For example, the issuer may sell one or more credit default swaps entitling the issuer to receive a stream of payments over the term of the swap agreements provided that no event of default has occurred with respect to the referenced debt obligation upon which the swap is based. If a default occurs, the stream of payments may stop and the issuer would be obligated to pay the counterparty the par (or other agreed upon value) of the referenced debt obligation.

     The use of credit derivatives is a highly specialized activity which involves strategies and risks different from those associated with ordinary portfolio security transactions. If the Manager is incorrect in its forecasts of default risks, market spreads or other applicable factors, or a counterparty defaults, the investment performance of the Fund would diminish compared with what it would have been if these techniques were not used. In addition, it is possible that developments in the credit derivatives market, including potential government regulation, could adversely affect the Fund’s ability to terminate existing swap or other credit derivative agreements or to realize amounts to be received under such agreements.

     The Fund will enter into swap and other credit derivatives transactions only when the Manager believes it would be in the best interests of the Fund to do so. In addition, the Fund will enter into swap and other credit derivative agreements only with counterparties that meet certain standards of creditworthiness (generally, such counterparties would have to be eligible counterparties under the terms of the Fund’s repurchase agreement guidelines).