-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 VDwXTJvKM7ct4HdLaLInxPPXiCJVPp42P4IAEugRyEzcpFKngb6XvmUR2bGt+Zo4
 UDegKVAOJyTzmAc05pCTMw==

<SEC-DOCUMENT>0001275213-07-000002.txt : 20070502
<SEC-HEADER>0001275213-07-000002.hdr.sgml : 20070502
<ACCEPTANCE-DATETIME>20070502164638
ACCESSION NUMBER:		0001275213-07-000002
CONFORMED SUBMISSION TYPE:	4/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20061201
FILED AS OF DATE:		20070502
DATE AS OF CHANGE:		20070502

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CLINE DAVID E
		CENTRAL INDEX KEY:			0001275213

	FILING VALUES:
		FORM TYPE:		4/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-13823
		FILM NUMBER:		07811277

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		336.626.8300

	MAIL ADDRESS:	
		STREET 1:		610 ENNIS ROAD
		CITY:			WAXHAW
		STATE:			NC
		ZIP:			28173

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			FNB United Corp.
		CENTRAL INDEX KEY:			0000764811
		STANDARD INDUSTRIAL CLASSIFICATION:	NATIONAL COMMERCIAL BANKS [6021]
		IRS NUMBER:				561456589
		STATE OF INCORPORATION:			NC
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		150 SOUTH FAYETTEVILLE STREET
		STREET 2:		P O BOX 1328
		CITY:			ASHEBORO
		STATE:			NC
		ZIP:			27203
		BUSINESS PHONE:		3366268300

	MAIL ADDRESS:	
		STREET 1:		P.O. BOX 1328
		CITY:			ASHEBORO
		STATE:			NC
		ZIP:			27204

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	FNB CORP/NC
		DATE OF NAME CHANGE:	19920703
</SEC-HEADER>
<DOCUMENT>
<TYPE>4/A
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2006-12-01</periodOfReport>

    <dateOfOriginalSubmission>2006-12-01</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000764811</issuerCik>
        <issuerName>FNB United Corp.</issuerName>
        <issuerTradingSymbol>FNBN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001275213</rptOwnerCik>
            <rptOwnerName>CLINE DAVID E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>610 ENNIS ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>WAXHAW</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>28173</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-12-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.8533</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>15642</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-12-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2112</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.85</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13530</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">On December 15, 2006, the reporting person filed a Form 4 mistakenly reporting purchases of Common Stock.  These should have been reported as sales of Common Stock.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Chandalar McMillian, Attorney in Fact</signatureName>
        <signatureDate>2007-05-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----