<PAGE>
PROSECUTES SUPPLEMENT to Filed Pursuant to Rule 424(b)(3)
PROSPECTUS dated October 1, 1999 Registration No. 333-81229
7,000,000 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 7,000,000 shares of Class A common stock of
Adelphia. This prospectus supplement is being provided to update certain
information contained in the selling stockholder table found on page 22 of the
original prospectus with respect to the insertion of Robert Grote III, Personal
Representative, The Estate of Roger S. Ahlbrandt as a replacement for Roger S.
Ahlbrandt as a selling stockholder under the prospectus.
The following table sets forth a revised selling stockholder information:
<TABLE>
<CAPTION>
Maximum Number of Shares of Class A
-----------------------------------
Selling Stockholder Common Stock That May Be Resold
------------------- -------------------------------
<S> <C>
Robert Grote III, Personal Representative, 3,451
The Estate of Roger S. Ahlbrandt
Total 3,451
</TABLE>
The date of this Prospectus Supplement is July 6, 2000.
