-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 QgDk860xCoXFYgkBiZW4oTPZ2W6d8QRw1f6ebWnAhZ3YE1SAiBzFO3CKNgEKHJRu
 76k77n0G1z0C4H4rg1RnFg==

<SEC-DOCUMENT>0001179110-05-008133.txt : 20050426
<SEC-HEADER>0001179110-05-008133.hdr.sgml : 20050426
<ACCEPTANCE-DATETIME>20050426102547
ACCESSION NUMBER:		0001179110-05-008133
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050331
FILED AS OF DATE:		20050426
DATE AS OF CHANGE:		20050426

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			GENAISSANCE PHARMACEUTICALS INC
		CENTRAL INDEX KEY:			0001110009
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMMERCIAL PHYSICAL & BIOLOGICAL RESEARCH [8731]
		IRS NUMBER:				061338846
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		FIVE SCIENCE PARK
		CITY:			NEW HAVEN
		STATE:			CT
		ZIP:			06511
		BUSINESS PHONE:		2037731450

	MAIL ADDRESS:	
		STREET 1:		FIVE SCIENCE PARK
		CITY:			NEW HAVEN
		STATE:			CT
		ZIP:			06511

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			PENNER HARRY JR
		CENTRAL INDEX KEY:			0001131148

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30981
		FILM NUMBER:		05771816

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		2037731450

	MAIL ADDRESS:	
		STREET 1:		C/O GENAISSANCE PHARMACEUTICALS
		STREET 2:		5 SCIENCE PARK
		CITY:			NEW HAVEN
		STATE:			CT
		ZIP:			06511
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-03-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001110009</issuerCik>
        <issuerName>GENAISSANCE PHARMACEUTICALS INC</issuerName>
        <issuerTradingSymbol>GNSC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001131148</rptOwnerCik>
            <rptOwnerName>PENNER HARRY JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GENAISSANCE PHARMACEUTICALS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>FIVE SCIENCE PARK</rptOwnerStreet2>
            <rptOwnerCity>NEW HAVEN</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06511</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>12800</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>32800</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/ Ben D. Kaplan as POA for Harry Penner Jr.</signatureName>
        <signatureDate>2005-04-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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