<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-02-26</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001012270</issuerCik>
        <issuerName>COLLAGENEX PHARMACEUTICALS INC</issuerName>
        <issuerTradingSymbol>CGPI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001304113</rptOwnerCik>
            <rptOwnerName>Powell Andrew Kenneth William</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>COLLAGENEX PHARMACEUTICALS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>41 UNIVERSITY DRIVE, SUITE 200</rptOwnerStreet2>
            <rptOwnerCity>NEWTOWN</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>18940</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP, G. Counsel and Corp. Sec.</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Options to Purchase Common Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>14.28</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-02-26</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>25000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2008-02-26</value>
            </exerciseDate>
            <expirationDate>
                <value>2017-02-25</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>25000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1257000</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents options granted by the Issuer pursuant to its 2005 Equity Incentive Plan on February 26, 2007. The options vest as follows: 5,000 shares subject to such options vest on February 26, 2008, 5,000 shares subject to such options vest on February 26, 2009, 5,000 shares subject to such options vest on February 26, 2010, 5,000 shares subject to such options vest on February 26, 2011 and 5,000 shares subject to such options vest on February 9, 2012.</footnote>
        <footnote id="F2">Includes multiple options grants with different prices and vesting dates.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Andrew K.W. Powell</signatureName>
        <signatureDate>2007-03-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
