<PAGE>
Filed Pursuant to Rule 424(b)(3)
Registration No. 333-86257
Supplement, Dated November 10, 1999, to Prospectus, Dated September 17, 1999, of
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UnitedGlobalCom, Inc.
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Additional Selling Securityholders. The following selling securityholders are
added to the list of sellilng securityholders in the prospectus:
<TABLE>
<CAPTION>
Number of Depositary Shares
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Name of Selling Securityholder Owned Offered
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<S> <C> <C>
GLG Market Neutral Fund............................ 63,500 63,500
Mainstay Convertible Fund.......................... 84,000 84,000
Mainstay VP Convertible Fund....................... 8,500 8,500
New York Life Separate Account #7.................. 8,500 8,500
</TABLE>
