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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-03-02</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001076930</issuerCik>
        <issuerName>GSI GROUP INC</issuerName>
        <issuerTradingSymbol>GSIG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000923910</rptOwnerCik>
            <rptOwnerName>BERSHAD STEPHEN W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>PO BOX 31100</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SANTA FE, NM</rptOwnerCity>
            <rptOwnerState>NM</rptOwnerState>
            <rptOwnerZipCode>87594</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-03-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>128474</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4123482</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">On July 23, 2010 (the &quot;Effective Date&quot;), the Final Fourth Modified Joint Chapter 11 Plan of Reorganization for MES International Inc. (&quot;MES&quot;), GSI Group Inc. (the &quot;Company)&quot; and GSI Group Corporation (&quot;GSI and, collectively with MES and the Company, the &quot;Debtors&quot;), as confirmed by the United States Bankruptcy Court for the District of Delaware on May 27, 2010 (the &quot;Plan&quot;), became effective and the Debtors emerged from Chapter 11 protection.   In connection with the Plan, (i) all common shares and vested share rights of the Company that were outstanding prior to the Effective Date (collectively, the &quot;Old Common Shares&quot;) were cancelled and (ii) new common shares of the Company, as reorganized (&quot;New Common Shares&quot;), were issued to holders of such Old Common Shares under the Final Plan on a one-for-one basis, subject to a 6.165% escrow as contemplated in the Plan.   On March 2, 2011, the New Common Shaers subject to the 6.165% escrow were rleased to the Reporting Person.</footnote>
        <footnote id="F2">Reflects the Company's 1 for 3 reverse stock split effecutated on December 29, 2010.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Anthony J. Bellantuoni, Attorney-in-Fact (POA on file)</signatureName>
        <signatureDate>2011-03-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
