<SEC-DOCUMENT>0001179110-12-017719.txt : 20121214
<SEC-HEADER>0001179110-12-017719.hdr.sgml : 20121214
<ACCEPTANCE-DATETIME>20121214192112
ACCESSION NUMBER:		0001179110-12-017719
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20121214
FILED AS OF DATE:		20121214
DATE AS OF CHANGE:		20121214

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			RODRIGUEZ RITA M
		CENTRAL INDEX KEY:			0001195477

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-13459
		FILM NUMBER:		121266999

	MAIL ADDRESS:	
		STREET 1:		3075 ORDWAY STREET NW
		CITY:			WASHINGTON
		STATE:			DC
		ZIP:			20008

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			AFFILIATED MANAGERS GROUP INC
		CENTRAL INDEX KEY:			0001004434
		STANDARD INDUSTRIAL CLASSIFICATION:	INVESTMENT ADVICE [6282]
		IRS NUMBER:				043218510
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		600 HALE STREET
		STREET 2:		/
		CITY:			PRIDES CROSSING
		STATE:			MA
		ZIP:			01965
		BUSINESS PHONE:		6177473300

	MAIL ADDRESS:	
		STREET 1:		600 HALE STREET
		STREET 2:		/
		CITY:			PRIDES CROSSING
		STATE:			MA
		ZIP:			01965
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-12-14</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001004434</issuerCik>
        <issuerName>AFFILIATED MANAGERS GROUP INC</issuerName>
        <issuerTradingSymbol>AMG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001195477</rptOwnerCik>
            <rptOwnerName>RODRIGUEZ RITA M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O AFFILIATED MANAGERS GROUP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>600 HALE STREET</rptOwnerStreet2>
            <rptOwnerCity>PRIDES CROSSING</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01965</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Director Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>127.91</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-12-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1411</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>127.91</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2016-12-31</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-12-14</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1411</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1411</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Units</value>
                <footnoteId id="F2"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-12-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>313</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2017-01-01</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>313</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>313</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This option is exercisable in 25% increments on each of December 31, 2013, 2014, 2015 and 2016.  The exercisability of this option would be accelerated upon a change of control of the Company.</footnote>
        <footnote id="F2">Represents stock units granted to the reporting person under the Company's Deferred Compensation Plan.  Each stock unit represents a right to receive one share of the Company's common stock or, at the election of the plan administrator, cash with an equivalent value, upon vesting.  The stock units vest in 25% increments on each of January 1, 2014, 2015, 2016 and 2017.  The vesting of the stock units would be accelerated upon a change of control of the Company.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ John Kingston, III, Attorney-in-Fact</signatureName>
        <signatureDate>2012-12-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
