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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-05-03</periodOfReport>

    <issuer>
        <issuerCik>0001088033</issuerCik>
        <issuerName>QUEST SOFTWARE INC</issuerName>
        <issuerTradingSymbol>QSFT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001106661</rptOwnerCik>
            <rptOwnerName>DOYLE DAVID M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O QUEST SOFTWARE, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>8001 IRVINE CENTER DRIVE</rptOwnerStreet2>
            <rptOwnerCity>IRVINE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92618</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Futures Contract (obligation to sell)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-05-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>200000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2006-05-03</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2006-05-03</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>200000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>200000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Mr. Doyle entered into a pre-paid variable delivery forward contract relating to 200,000 shares of the issuer's common stock (&quot;Common Stock&quot;).  In exchange for a cash payment of $2,089,547, Mr. Doyle agreed to deliver a number of shares of Common Stock in May 2006 (subject to earlier termination) pursuant to the following formula: (i) if the price of Common Stock in May 2006 (the &quot;Settlement Value&quot;) is less than or equal to $11.8455 (the &quot;Floor&quot;), 200,000 shares; (ii) if the Settlement Value is less than or equal to $14.2146 (the &quot;Threshold&quot;), but greater than the Floor, then a number of shares equal to 200,000 shares multiplied by the Floor divided by the Settlement Value; and (iii) if the Settlement Value is greater than the Threshold, then such number of shares as determined by a formula set forth in the contract. Alternatively, Mr. Doyle may settle this contract for an amount of cash equal to the number of shares required to be delivered multiplied by the Settlement Value.</footnote>
        <footnote id="F2">This transaction was effected pursuant to a 10b5-1 trading plan adopted by the reporting person on March 5, 2004.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>J. Michael Vaughn, Attorney-in-Fact for David M. Doyle</signatureName>
        <signatureDate>2004-05-05</signatureDate>
    </ownerSignature>
</ownershipDocument>

