<SEC-DOCUMENT>0000890564-17-000039.txt : 20170215
<SEC-HEADER>0000890564-17-000039.hdr.sgml : 20170215
<ACCEPTANCE-DATETIME>20170215183725
ACCESSION NUMBER:		0000890564-17-000039
CONFORMED SUBMISSION TYPE:	4/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20170209
FILED AS OF DATE:		20170215
DATE AS OF CHANGE:		20170215

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ON ASSIGNMENT INC
		CENTRAL INDEX KEY:			0000890564
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-HELP SUPPLY SERVICES [7363]
		IRS NUMBER:				954023433
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		26745 MALIBU HILLS ROAD
		CITY:			CALABASAS
		STATE:			CA
		ZIP:			91301
		BUSINESS PHONE:		8188787900

	MAIL ADDRESS:	
		STREET 1:		26745 MALIBU HILLS ROAD
		CITY:			CALABASAS
		STATE:			CA
		ZIP:			91301

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BLAZER RANDOLPH C
		CENTRAL INDEX KEY:			0001206876

	FILING VALUES:
		FORM TYPE:		4/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-35636
		FILM NUMBER:		17615962

	MAIL ADDRESS:	
		STREET 1:		26745 MALIBU HILLS ROAD
		CITY:			CALABASAS
		STATE:			CA
		ZIP:			91301
</SEC-HEADER>
<DOCUMENT>
<TYPE>4/A
<SEQUENCE>1
<FILENAME>wf-form4a_148720183204752.xml
<DESCRIPTION>FORM 4/A
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2017-02-09</periodOfReport>

    <dateOfOriginalSubmission>2017-02-13</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000890564</issuerCik>
        <issuerName>ON ASSIGNMENT INC</issuerName>
        <issuerTradingSymbol>ASGN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001206876</rptOwnerCik>
            <rptOwnerName>BLAZER RANDOLPH C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2>26745 MALIBU HILLS ROAD</rptOwnerStreet2>
            <rptOwnerCity>CALABASAS</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>91301</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Pres, Apex-a sub of the Issuer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2017-02-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>10284</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>82950</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This amendment of the Form 4 filed for the executive officer on 2/13/17 amends the ninth transaction listed by adding an additional 3,428 restricted stock units to that line item.</footnote>
        <footnote id="F2">On February 9, 2017 performance targets were achieved for an RSU grant that was previously made to the executive officer. 50% of these RSU's will vest on January 2, 2018 and the remaining RSU's will vest on January 2, 2019, subject to the executive officer's continued service to the Company.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>By: /s/ Jennifer Painter, CLO  For: Randolph C. Blazer</signatureName>
        <signatureDate>2017-02-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
