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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-05-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000731012</issuerCik>
        <issuerName>HEALTHCARE SERVICES GROUP INC</issuerName>
        <issuerTradingSymbol>HCSG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001210672</rptOwnerCik>
            <rptOwnerName>MCCARTNEY DANIEL P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3220 TILLMAN DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 300</rptOwnerStreet2>
            <rptOwnerCity>BENSALEM</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19020</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-05-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>113901</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>45.8676</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1968223</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Amount of Securities Beneficially Owned in the Form 4 filed by the Reporting Person on November 25, 2016 did not include an aggregate of 74,880 shares that the Reporting Person received as part of the conversion of phantom stock into 74,880 shares of common stock pursuant to the Issuer's Deferred Compensation Plan. Such conversions are exempt from Section 16(b) pursuant to Rule 16b-6(b).</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ John C. Shea, by Power of Attorney</signatureName>
        <signatureDate>2017-05-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2017-05-11
0
0000731012
HEALTHCARE SERVICES GROUP INC
HCSG
0001210672
MCCARTNEY DANIEL P
3220 TILLMAN DRIVE
SUITE 300
BENSALEM
PA
19020
1
0
0
0
Common Stock
2017-05-11
4
S
0
113901
45.8676
D
1968223
D
Amount of Securities Beneficially Owned in the Form 4 filed by the Reporting Person on November 25, 2016 did not include an aggregate of 74,880 shares that the Reporting Person received as part of the conversion of phantom stock into 74,880 shares of common stock pursuant to the Issuer's Deferred Compensation Plan. Such conversions are exempt from Section 16(b) pursuant to Rule 16b-6(b).
/s/ John C. Shea, by Power of Attorney
2017-05-15