<PAGE>
PROSPECTUS 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 revise certain
information contained in the selling stockholder table found on page 22 of the
original prospectus with respect to the number of shares held by Duff Ackerman
Goodrich, LLC, Donald F. Bogue and Linda A. Bogue Trust, UTA 6/4/96, Daniel I.
Booker, Daniel R. Duff, John M. Duff, Jr., R. Thomas Goodrich, John M. Noerr,
William M. Robinson and Leonard Schwarz:
The following table sets forth a revised number of shares held by such
selling stockholders (the revised amounts are set forth opposite each selling
stockholder's name):
<TABLE>
<CAPTION>
Selling Stockholder Number of Shares of Class A Common Stock
------------------- ----------------------------------------
<S> <C>
Donald F. Bogue and 1,195
Linda A. Bogue Trust, UTA 6/4/96
Daniel I. Booker 1,494
Daniel R. Duff 1,793
John M. Duff 14,375
R. Thomas Goodrich 10,164
John M. Noerr 3,334
William M. Robinson 4,649
Leonard Schwarz 1,793
-----
Total
</TABLE>
Duff Ackerman Goodrich, LLC, who was listed as a selling stockholder in the
original prospectus, is not a selling stockholder under this prospectus. This
supplement should be retained with your prospectus.
The date of this Prospectus Supplement is November 2, 1999.
