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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-06-03</periodOfReport>

    <issuer>
        <issuerCik>0001014739</issuerCik>
        <issuerName>BioScrip, Inc.</issuerName>
        <issuerTradingSymbol>BIOS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001286630</rptOwnerCik>
            <rptOwnerName>GOLDING DAVID W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O BIOSCRIP INC.</rptOwnerStreet1>
            <rptOwnerStreet2>1600 BROADWAY, SUITE 950</rptOwnerStreet2>
            <rptOwnerCity>DENVER</rptOwnerCity>
            <rptOwnerState>CO</rptOwnerState>
            <rptOwnerZipCode>80202</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Cash-Settled Restricted Stock Unit</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2019-06-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18905</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, $.0001 Par Value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>18905</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18905</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each Cash-Settled Restricted Stock Unit (&quot;Cash-Settled RSU&quot;) is the economic equivalent of one share of BioScrip common stock. Upon vesting, each Cash-Settled RSU will entitle the awardee to a cash-payment equal to the &quot;Fair Market Value&quot; (as defined in the Company's 2018 Equity Incentive Plan (the &quot;Plan&quot;)) of one share of BioScrip common stock on the vesting date.</footnote>
        <footnote id="F2">The Cash-Settled RSUs vest and become non-forfeitable on the earlier of (1) the consummation of a Change of Control (as defined in the Plan), and (2) the day before the Company's 2020 Annual Meeting, provided the awardee has remained in continuous service as a member of the Company's Board of Directors through such date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ David W. Golding</signatureName>
        <signatureDate>2019-06-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
