<PAGE>
Filed Pursuant to Rule 424(b)(3)
Registration No.: 333-86257
Supplement, Dated January 6, 2000, to Prospectus, Dated September 17, 1999,
- ---------------------------------------------------------------------------
of UnitedGlobalCom, Inc.
- ------------------------
Additional Selling Securityholders. The following selling securityholders are
added to the list of selling securityholders in the prospectus:
<TABLE>
<CAPTION>
Number of Depositary Shares
---------------------------
Owned Offered
------------- ------------
Name of Selling Securityholder
- ------------------------------
<S> <C> <C>
Donaldson, Lufkin & Jenrette Securities Corporation............. 80,000 80,000
Susquehanna Capital Group....................................... 25,000 25,000
</TABLE>
Donaldson, Lufkin & Jenrette Securities Corporation was an initial purchaser in
the June 1999 private placement offering through which the selling
securityholders acquired their shares, resulting in a material relationship
between us and Donaldson, Lufkin & Jenrette Securities Corporation.
