<SUBMISSION>
<ACCESSION-NUMBER>0000859737-06-000015
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20060503
<FILING-DATE>20060505
<DATE-OF-FILING-DATE-CHANGE>20060505
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>HOLOGIC INC
<CIK>0000859737
<ASSIGNED-SIC>3844
<IRS-NUMBER>042902449
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>0930
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>35 CROSBY DRIVE
<CITY>BEDFORD
<STATE>MA
<ZIP>01730
<PHONE>7819997300
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>35 CROSBY DRIVE
<CITY>BEDFORD
<STATE>MA
<ZIP>01730
</MAIL-ADDRESS>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>MUIR GLENN P
<CIK>0001181190
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-18281
<FILM-NUMBER>06810948
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>C/O HOLOGIC
<STREET2>35 CROSBY DRIVE
<CITY>BEDFORD
<STATE>MA
<ZIP>01730
<PHONE>7819997377
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>35 CROSBY DRIVE
<CITY>BEDFORD
<STATE>MA
<ZIP>01730
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-05-03</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000859737</issuerCik>
        <issuerName>HOLOGIC INC</issuerName>
        <issuerTradingSymbol>HOLX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001181190</rptOwnerCik>
            <rptOwnerName>MUIR GLENN P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>35 CROSBY DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BEDFORD</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01730</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Executive VP &amp; CFO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Unit Award (Right to Receive)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>46.38</value>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-05-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10781</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2008-12-31</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2008-12-31</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>10781</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10781</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The restricted stock unit award converts to shares of common stock on a 1-for-1 basis.</footnote>
        <footnote id="F2">The restricted stock units have been granted under Hologic's Amended and Restated 1999 Equity Incentive Plan.  The restricted stock units will become 100% vested on December 31, 2008 (the &quot;Restrictions Lapse Date&quot;) only if the reporting person remains employed by the Company in the positions set forth in the reporting person's retention and severance agreement at all times prior to Restrictions Lapse Date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Glenn Muir</signatureName>
        <signatureDate>2006-05-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
