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

    <schemaVersion>X0203</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2010-08-05</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000722723</issuerCik>
        <issuerName>HANGER ORTHOPEDIC GROUP INC</issuerName>
        <issuerTradingSymbol>HGR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001498511</rptOwnerCik>
            <rptOwnerName>Morton Andrew C.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HANGER ORTHOPEDIC GROUP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>10910 DOMAIN DRIVE, SUITE 300</rptOwnerStreet2>
            <rptOwnerCity>AUSTIN</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>78758</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>V.P.-Human Resources</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12000</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The reporting person's appointment as Vice President-Human Resources of the issuer was approved by the issuer's Board of Directors on August 5, 2010. The shares reported on Table I include unvested restricted shares previously issued in accordance with Rule 16b-3 under the Securities Exchange Act of 1934 that total 12,000 shares of stock from an original grant of 12,000 shares of restricted stock made on June 21, 2010, of which 25% of the shares vest on June 21, 2011 and which cumulatively vest to the extent of 25% each year thereafter.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Teri L. Champ, Attorney-in-Fact for Andrew C. Morton</signatureName>
        <signatureDate>2010-08-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
