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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 BSkfhRqG0V1t8oazy8zc2LvKKyUD09nIBHf6k5ZHGa57lwOa1w0BrvBppYcbfxsC
 A/Us3RisSbs4JQ18FCoqiw==

<SEC-DOCUMENT>0001209191-04-059286.txt : 20041223
<SEC-HEADER>0001209191-04-059286.hdr.sgml : 20041223
<ACCEPTANCE-DATETIME>20041223113731
ACCESSION NUMBER:		0001209191-04-059286
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20041214
FILED AS OF DATE:		20041223
DATE AS OF CHANGE:		20041223

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			IMPSAT FIBER NETWORKS INC
		CENTRAL INDEX KEY:			0001022329
		STANDARD INDUSTRIAL CLASSIFICATION:	COMMUNICATION SERVICES, NEC [4899]
		IRS NUMBER:				521910372
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		ELVIRA RAWSON DE DELLEPIANE 150
		STREET 2:		PISO 8
		CITY:			BUENOS AIRES
		STATE:			C1
		ZIP:			C1107BCA
		BUSINESS PHONE:		54115170000

	MAIL ADDRESS:	
		STREET 1:		ELVIRA RAWSON DE DELLEPIANE 150
		STREET 2:		PISO 8
		CITY:			BUENOS AIRES
		STATE:			C1
		ZIP:			C1107BCA

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	IMPSAT CORP
		DATE OF NAME CHANGE:	19960905

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			UBS AG
		CENTRAL INDEX KEY:			0001114446
		STANDARD INDUSTRIAL CLASSIFICATION:	NATIONAL COMMERCIAL BANKS [6021]
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-29085
		FILM NUMBER:		041222980

	BUSINESS ADDRESS:	
		STREET 1:		BAHNHOFSTRASSE 45
		STREET 2:		P O BOX CH 8098
		CITY:			ZURICH
		STATE:			V8
		ZIP:			-
		BUSINESS PHONE:		41-1-234-4100

	MAIL ADDRESS:	
		STREET 1:		BAHNHOFSTRASSE 45
		STREET 2:		P O BOX CH 8098
		CITY:			ZURICH
		STATE:			V8
		ZIP:			-
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>bny69674_ubs.xml
<DESCRIPTION>MAIN DOCUMENT DESCRIPTION
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2004-12-14</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001022329</issuerCik>
        <issuerName>IMPSAT FIBER NETWORKS INC</issuerName>
        <issuerTradingSymbol>IMFN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001114446</rptOwnerCik>
            <rptOwnerName>UBS AG</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>677 WASHINGTON BLVD.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>STAMFORD</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1202380</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <ownerSignature>
        <signatureName>/s/ Per Dyrvik, Managing Director, /s/ David Aufhauser, Managing Director</signatureName>
        <signatureDate>2004-12-17</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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