<PAGE>
Filed Pursuant to Rule 424(b)(3)
Registration No. 333-84119
PROSPECTUS SUPPLEMENT to
PROSPECTUS dated October 1, 1999
1,852,302 shares
ADELPHIA COMMUNICATIONS CORPORATION
Class A common stock
This prospectus supplement relates to the prospectus dated October 1, 1999
regarding the sale of up to 1,852,302 shares of Class A common stock of
Adelphia. This prospectus supplement is being provided to reflect the transfer
by Citizens Cable Company, the selling stockholder named in the October 1, 1999
prospectus, of 1,852,302 shares of Class A common stock held by it to
Southwestern Capital Corporation, a wholly owned subsidiary of Citizens
Utilities Company. Citizens Utilities Company is the ultimate parent company of
both Citizens Cable Company and Southwestern Capital Corporation. This transfer
was made without the receipt of any consideration to Citizens Cable Company and
after the registration statement to which the October 1, 1999 prospectus is a
part was made effective.
The information contained in the original selling stockholder table can be found
on page 20 of the October 1, 1999 prospectus.
The following table sets forth as of January 31, 2000 the revisions to the
original selling stockholder table.
<TABLE>
<CAPTION>
Number of Shares
of Class A % of Class A Class A Common
Common Before Held Before Share Offering
Selling Stockholder Offering Offering Hereby
------------------- -------- -------- ------
<S> <C> <C> <C>
Southwestern Capital Corporation 1,852,302 1.7% 1,852,302
--------- ---- ---------
Total 1,852,302 1.7% 1,852,302
========= ==== =========
</TABLE>
The date of this Prospectus Supplement is February 4, 2000.
