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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 CpdlspFnRU7pf1PPjaO+xpricmYjW9FCn5QbaQnMqRnMNDi6zI1JvAp2LW7hnvEj
 leRPkpfOZYtxvPrALikUug==

<SEC-DOCUMENT>0001179110-08-001471.txt : 20080122
<SEC-HEADER>0001179110-08-001471.hdr.sgml : 20080121
<ACCEPTANCE-DATETIME>20080122161508
ACCESSION NUMBER:		0001179110-08-001471
CONFORMED SUBMISSION TYPE:	4/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080102
FILED AS OF DATE:		20080122
DATE AS OF CHANGE:		20080122

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Sirtris Pharmaceuticals, Inc.
		CENTRAL INDEX KEY:			0001388775
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				201410189
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		SUITE 104
		STREET 2:		790 MEMORIAL DRIVE
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		617-252-6920

	MAIL ADDRESS:	
		STREET 1:		SUITE 104
		STREET 2:		790 MEMORIAL DRIVE
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	Sirtris Pharmaceuticals
		DATE OF NAME CHANGE:	20070202

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Jirousek Michael
		CENTRAL INDEX KEY:			0001394939

	FILING VALUES:
		FORM TYPE:		4/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-33465
		FILM NUMBER:		08542063

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		617-252-6924

	MAIL ADDRESS:	
		STREET 1:		C/O SIRTRIS PHARMACEUTICALS, INC.
		STREET 2:		790 MEMORIAL DR. SUITE 104
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
</SEC-HEADER>
<DOCUMENT>
<TYPE>4/A
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4/A -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2008-01-02</periodOfReport>

    <dateOfOriginalSubmission>2008-01-04</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001388775</issuerCik>
        <issuerName>Sirtris Pharmaceuticals, Inc.</issuerName>
        <issuerTradingSymbol>SIRT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001394939</rptOwnerCik>
            <rptOwnerName>Jirousek Michael</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SIRTRIS PHARMACEUTICALS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>200 TECHNOLOGY SQUARE</rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02139</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior VP, Research</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-01-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>32500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>32500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Incentive Stock Option (Right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>13.00</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2008-01-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>32500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2018-01-02</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>32500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>32500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The options shall vest as to 25% on January 2, 2009, with the remainder to vest in equal quarterly installments over the next 12 quarters ending April 2, July 2, and October 2 following January 2, 2009.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Marc Rubenstein, Attorney-in-fact</signatureName>
        <signatureDate>2008-01-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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