<?xml version="1.0"?>

<ownershipDocument>

    <schemaVersion>X0201</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2003-08-22</periodOfReport>

    <dateOfOriginalSubmission>2003-08-22</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000069499</issuerCik>
        <issuerName>MYLAN LABORATORIES INC</issuerName>
        <issuerTradingSymbol>MYL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001197542</rptOwnerCik>
            <rptOwnerName>BORKOWSKI EDWARD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>MYLAN PHARMACEUTICALS INC</rptOwnerStreet1>
            <rptOwnerStreet2>781 CHESTNUT RIDGE RD</rptOwnerStreet2>
            <rptOwnerCity>MORGANTOWN</rptOwnerCity>
            <rptOwnerState>WV</rptOwnerState>
            <rptOwnerZipCode>26505</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>

        <nonDerivativeTransaction>
            <securityTitle>
                <value>Mylan Laboratories Inc. Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2003-08-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>30000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>30000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>

    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The Reporting Person was granted restricted stock pursuant to the Mylan Laboratories Inc. 2003 Long-Term Incentive Plan. The shares vest on August 21, 2006 (previously inadvertently reported as 2005). Mylan Laboratories Inc. common stock Indirect ownership through 401(k) holdings was 327 shares as of August 21, 2003.</footnote>
    </footnotes>


    <ownerSignature>
        <signatureName>Edward J. Borkowski</signatureName>
        <signatureDate>2003-08-22</signatureDate>
    </ownerSignature>

</ownershipDocument>

