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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2022-01-04</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001890359</rptOwnerCik>
            <rptOwnerName>Simmons Kurt JR</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>2022-01-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1289</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>18.10</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1289</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents a grant of unvested deferred stock units (&quot;DSU&quot;) granted under the Issuer's 2020 Omnibus Incentive Plan which will become fully vested on May 31, 2022. Such DSUs will be settled in shares of common stock on the first to occur of (i) five-year anniversary of the Date of Grant, (ii) the Participant's date of death, disability or separation form service; or (iii) the date of a Change of Control (the &quot;Settlement Date&quot;). A Participant may elect a further deferral beyond the Settlement Date pursuant to the rules of Code Section 409A.</footnote>
        <footnote id="F2">Amount represents 1,289 unvested DSUs.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Andrew Brophy</signatureName>
        <signatureDate>2022-01-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2022-01-04
0
0000731012
HEALTHCARE SERVICES GROUP INC
HCSG
0001890359
Simmons Kurt JR
3220 TILLMAN DRIVE
SUITE 300
BENSALEM
PA
19020
1
0
0
0
Common Stock
2022-01-04
4
A
0
1289
18.10
A
1289
D
Represents a grant of unvested deferred stock units ("DSU") granted under the Issuer's 2020 Omnibus Incentive Plan which will become fully vested on May 31, 2022. Such DSUs will be settled in shares of common stock on the first to occur of (i) five-year anniversary of the Date of Grant, (ii) the Participant's date of death, disability or separation form service; or (iii) the date of a Change of Control (the "Settlement Date"). A Participant may elect a further deferral beyond the Settlement Date pursuant to the rules of Code Section 409A.
Amount represents 1,289 unvested DSUs.
Andrew Brophy
2022-01-05