<PAGE>

   As filed with the Securities and Exchange Commission on August 25, 1999
                                                      REGISTRATION NO. 333-_____
================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549
                           _________________________
                                   FORM S-8

                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933
                           _________________________

                               US ONCOLOGY, INC.
                 (formerly American Oncology Resources, Inc.)
            (Exact name of Registrant as specified in its charter)
<TABLE>
<CAPTION>
<S>                                    <C>                                        <C>
           Delaware                       16825 Northchase Drive, Suite 1300             84-1213501
(State or other jurisdiction                   Houston, Texas 77060                    (I.R.S. Employer
of incorporation or organization)      (Address of principal executive offices)       Identification No.)
                                                    (Zip Code)
</TABLE>
                           ________________________

                       AMERICAN ONCOLOGY RESOURCES, INC.
                 1993 NON-EMPLOYEE DIRECTOR STOCK OPTION PLAN
                           (Full title of the plan)
                          __________________________
                               Phillip H. Watts
                                General Counsel
                               US Oncology, Inc.
                      16825 Northchase Drive, Suite 1300
                             Houston, Texas  77060
                    (Name and address of agent for service)

                                (281) 873-2674
         (Telephone number, including area code, of agent for service)
                         _____________________________
                                   Copy to:
                                Diana M. Hudson
                     Mayor, Day, Caldwell & Keeton, L.L.P.
                           700 Louisiana, Suite 1900
                             Houston, Texas  77002
                                (713) 225-7100
                         _____________________________
                        CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
====================================================================================================================================
           TITLE OF                 AMOUNT TO BE    PROPOSED MAXIMUM OFFERING    PROPOSED MAXIMUM AGGREGATE   AMOUNT OF REGISTRATION
  SECURITIES TO BE REGISTERED        REGISTERED        PRICE PER SHARE(1)             OFFERING PRICE(1)                FEE
------------------------------------------------------------------------------------------------------------------------------------
<S>                                           <C>            <C>                             <C>                             <C>
Common Stock,
par value $.01 per share (2)          399,600             $10.56                          $4,220,775                 $1,174
====================================================================================================================================
</TABLE>
(1)  Estimated solely for the purpose of calculating the registration fee
     pursuant to Rule 457(c).
(2)  Including an equal number of Series A Preferred Stock Purchase Rights
     associated with the Common Stock.
================================================================================
<PAGE>

   INCORPORATION OF CONTENTS OF EARLIER REGISTRATION STATEMENT BY REFERENCE

     The contents of earlier registration statement, file number 333-778, are
incorporated by reference and made a part hereof.
<PAGE>

                                  SIGNATURES

     PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THE REGISTRANT
CERTIFIES THAT IT HAS REASONABLE GROUNDS TO BELIEVE THAT IT MEETS ALL OF THE
REQUIREMENTS FOR FILING ON FORM S-8 AND HAS DULY CAUSED THIS REGISTRATION
STATEMENT TO BE SIGNED ON ITS BEHALF BY THE UNDERSIGNED, THEREUNTO DULY
AUTHORIZED, IN THE CITY OF HOUSTON, STATE OF TEXAS, ON AUGUST 12, 1999.

                              US ONCOLOGY, INC.


                              By: /s/ L. FRED POUNDS
                                  ---------------------------------------
                                  L. Fred Pounds
                                  Vice President of Finance and Treasurer

                               POWER OF ATTORNEY

     Each of the undersigned directors and officers of US Oncology, Inc. does
hereby constitute and appoint L. Fred Pounds as the undersigned's true and
lawful attorney-in-fact and agent to do any and all acts and things in the
undersigned's name and behalf in the undersigned's capacities as director and/or
officer, and to execute any and all instruments for the undersigned and in the
undersigned's name in the capacities indicated below which such person or
persons may deem necessary or advisable to enable US Oncology, Inc. to comply
with the Securities Act of 1933, as amended, and any rules, regulations and
requirements of the Securities and Exchange Commission in connection with this
Registration Statement, including specifically, but not limited to, power and
authority to sign for the undersigned in the capacities indicated below any and
all amendments (including post-effective amendments) hereto, and the undersigned
does hereby ratify and confirm all that such person or persons shall do or cause
to be done by virtue hereof.

     PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THIS
REGISTRATION STATEMENT HAS BEEN SIGNED BY THE FOLLOWING PERSONS IN THE
CAPACITIES AND ON THE DATES INDICATED.

<TABLE>
<CAPTION>
        Signature                          Title                                Date
        ---------                          -----                                ----
<S>                               <C>                                <C>

/s/ R. DALE ROSS                  Chairman of the Board, Chief              August 9, 1999
-------------------------------   Executive Officer and Director
R. Dale Ross

/s/ L. FRED POUNDS                Vice President of Finance                 August 9, 1999
-------------------------------   and Treasurer
L. Fred Pounds

/s/ NANCY G. BRINKER              Director                                  August 9, 1999
-------------------------------
Nancy G. Brinker

/s/ RUSSELL L. CARSON             Director                                  August 9, 1999
-------------------------------
Russell L. Carson

/s/ JOHN T. CASEY                 Director                                  August 9, 1999
-------------------------------
John T. Casey
</TABLE>
                                       2
<PAGE>

<TABLE>
<CAPTION>

        Signature                          Title                                Date
        ---------                          -----                                ----
<S>                               <C>                                <C>

/s/ J. TAYLOR CRANDALL
-------------------------------   Director                                  August 9, 1999
J. Taylor Crandall

/s/ JAMES E. DALTON
-------------------------------   Director                                  August 9, 1999
James E. Dalton

/s/ ROBERT W. DALY
-------------------------------   Director                                  August 9, 1999
Robert W. Daly

/s/ STEPHEN E. JONES, M.D.
-------------------------------   Director                                  August 9, 1999
Stephen E. Jones, M.D.

/s/ STANLEY M. MARKS, M.D.
-------------------------------   Director                                  August 9, 1999
Stanley M. Marks, M.D.

/s/ RICHARD B. MAYOR
-------------------------------   Director                                  August 9, 1999
Richard B. Mayor

/s/ ROBERT A. ORTENZIO
-------------------------------   Director                                  August 9, 1999
Robert A. Ortenzio

/s/ BOONE POWELL, JR.
-------------------------------   Director                                  August 9, 1999
Boone Powell, Jr.

/s/ EDWARD E. ROGOFF, M.D.
-------------------------------   Director                                  August 9, 1999
Edward E. Rogoff, M.D.

/s/ BURTON S. SCHWARTZ, M.D.
-------------------------------   Director                                  August 9, 1999
Burton S. Schwartz, M.D.

</TABLE>

                                       3
<PAGE>

                                 EXHIBIT INDEX
                                 -------------
<TABLE>
<CAPTION>

 Exhibit No.                              Description
 -----------                              ------------
<C>              <S>
    4.1          Amended and Restated Certificate of Incorporation of the
                 Registrant - incorporated by reference from the Registrant's Form
                 8-K/A1 filed June 17, 1999.
    4.2          Amended and Restated By-Laws of the Registrant - incorporated by
                 reference from the Registrant's Form 8-K/A1 filed June 17, 1999.
    4.3          Rights Agreement between the Registrant and American Stock
                 Transfer & Trust Company - incorporated by reference to Exhibit 4
                 to Form 8-A of the Registrant filed June 2, 1997.
    4.4          American Oncology Resources, Inc., 1993 Non-Employee Director
                 Stock Option Plan, as amended.
      5          Opinion of Mayor, Day, Caldwell & Keeton, L.L.P.
   23.1          Consent of PricewaterhouseCoopers LLP.
   23.3          Consent of Mayor, Day, Caldwell & Keeton, L.L.P. (included in
                 Exhibit 5).
     24          Powers of Attorney (included on signature page of this
                 Registration Statement).
</TABLE>


                                       4
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 10062}]
{"company-data": {"conformed-name": "US ONCOLOGY INC", "cik": "0000943061", "assigned-sic": "8093", "irs-number": "841213501", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-85855", "film-number": "99699030"}, "business-address": {"street1": "16825 NORTHCHASE DR", "street2": "STE 1300", "city": "HOUSTON", "state": "TX", "zip": "77060", "phone": "2818732674"}, "former-company": {"former-conformed-name": "AMERICAN ONCOLOGY RESOURCES INC /DE/", "date-changed": "19950327"}}
As filed with the Securities and Exchange Commission on August 25, 1999
                                                      REGISTRATION NO. 333-_____
================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549
                           _________________________
                                   FORM S-8

                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933
                           _________________________

                               US ONCOLOGY, INC.
                 (formerly American Oncology Resources, Inc.)
            (Exact name of Registrant as specified in its charter)
Delaware                       16825 Northchase Drive, Suite 1300             84-1213501
(State or other jurisdiction                   Houston, Texas 77060                    (I.R.S. Employer
of incorporation or organization)      (Address of principal executive offices)       Identification No.)
                                                    (Zip Code)
________________________

                       AMERICAN ONCOLOGY RESOURCES, INC.
                 1993 NON-EMPLOYEE DIRECTOR STOCK OPTION PLAN
                           (Full title of the plan)
                          __________________________
                               Phillip H. Watts
                                General Counsel
                               US Oncology, Inc.
                      16825 Northchase Drive, Suite 1300
                             Houston, Texas  77060
                    (Name and address of agent for service)

                                (281) 873-2674
         (Telephone number, including area code, of agent for service)
                         _____________________________
                                   Copy to:
                                Diana M. Hudson
                     Mayor, Day, Caldwell & Keeton, L.L.P.
                           700 Louisiana, Suite 1900
                             Houston, Texas  77002
                                (713) 225-7100
                         _____________________________
                        CALCULATION OF REGISTRATION FEE
====================================================================================================================================
           TITLE OF                 AMOUNT TO BE    PROPOSED MAXIMUM OFFERING    PROPOSED MAXIMUM AGGREGATE   AMOUNT OF REGISTRATION
  SECURITIES TO BE REGISTERED        REGISTERED        PRICE PER SHARE(1)             OFFERING PRICE(1)                FEE
------------------------------------------------------------------------------------------------------------------------------------
Common Stock,
par value $.01 per share (2)          399,600             $10.56                          $4,220,775                 $1,174
====================================================================================================================================
(1)  Estimated solely for the purpose of calculating the registration fee
     pursuant to Rule 457(c).
(2)  Including an equal number of Series A Preferred Stock Purchase Rights
     associated with the Common Stock.
================================================================================
INCORPORATION OF CONTENTS OF EARLIER REGISTRATION STATEMENT BY REFERENCE

     The contents of earlier registration statement, file number 333-778, are
incorporated by reference and made a part hereof.
SIGNATURES

     PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THE REGISTRANT
CERTIFIES THAT IT HAS REASONABLE GROUNDS TO BELIEVE THAT IT MEETS ALL OF THE
REQUIREMENTS FOR FILING ON FORM S-8 AND HAS DULY CAUSED THIS REGISTRATION
STATEMENT TO BE SIGNED ON ITS BEHALF BY THE UNDERSIGNED, THEREUNTO DULY
AUTHORIZED, IN THE CITY OF HOUSTON, STATE OF TEXAS, ON AUGUST 12, 1999.

                              US ONCOLOGY, INC.

                              By: /s/ L. FRED POUNDS
                                  ---------------------------------------
                                  L. Fred Pounds
                                  Vice President of Finance and Treasurer

                               POWER OF ATTORNEY

     Each of the undersigned directors and officers of US Oncology, Inc. does
hereby constitute and appoint L. Fred Pounds as the undersigned's true and
lawful attorney-in-fact and agent to do any and all acts and things in the
undersigned's name and behalf in the undersigned's capacities as director and/or
officer, and to execute any and all instruments for the undersigned and in the
undersigned's name in the capacities indicated below which such person or
persons may deem necessary or advisable to enable US Oncology, Inc. to comply
with the Securities Act of 1933, as amended, and any rules, regulations and
requirements of the Securities and Exchange Commission in connection with this
Registration Statement, including specifically, but not limited to, power and
authority to sign for the undersigned in the capacities indicated below any and
all amendments (including post-effective amendments) hereto, and the undersigned
does hereby ratify and confirm all that such person or persons shall do or cause
to be done by virtue hereof.

     PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THIS
REGISTRATION STATEMENT HAS BEEN SIGNED BY THE FOLLOWING PERSONS IN THE
CAPACITIES AND ON THE DATES INDICATED.
Signature                          Title                                Date
        ---------                          -----                                ----
/s/ R. DALE ROSS                  Chairman of the Board, Chief              August 9, 1999
-------------------------------   Executive Officer and Director
R. Dale Ross

/s/ L. FRED POUNDS                Vice President of Finance                 August 9, 1999
-------------------------------   and Treasurer
L. Fred Pounds

/s/ NANCY G. BRINKER              Director                                  August 9, 1999
-------------------------------
Nancy G. Brinker

/s/ RUSSELL L. CARSON             Director                                  August 9, 1999
-------------------------------
Russell L. Carson

/s/ JOHN T. CASEY                 Director                                  August 9, 1999
-------------------------------
John T. Casey
2
Signature                          Title                                Date
        ---------                          -----                                ----
/s/ J. TAYLOR CRANDALL
-------------------------------   Director                                  August 9, 1999
J. Taylor Crandall

/s/ JAMES E. DALTON
-------------------------------   Director                                  August 9, 1999
James E. Dalton

/s/ ROBERT W. DALY
-------------------------------   Director                                  August 9, 1999
Robert W. Daly

/s/ STEPHEN E. JONES, M.D.
-------------------------------   Director                                  August 9, 1999
Stephen E. Jones, M.D.

/s/ STANLEY M. MARKS, M.D.
-------------------------------   Director                                  August 9, 1999
Stanley M. Marks, M.D.

/s/ RICHARD B. MAYOR
-------------------------------   Director                                  August 9, 1999
Richard B. Mayor

/s/ ROBERT A. ORTENZIO
-------------------------------   Director                                  August 9, 1999
Robert A. Ortenzio

/s/ BOONE POWELL, JR.
-------------------------------   Director                                  August 9, 1999
Boone Powell, Jr.

/s/ EDWARD E. ROGOFF, M.D.
-------------------------------   Director                                  August 9, 1999
Edward E. Rogoff, M.D.

/s/ BURTON S. SCHWARTZ, M.D.
-------------------------------   Director                                  August 9, 1999
Burton S. Schwartz, M.D.
3
EXHIBIT INDEX
                                 -------------
Exhibit No.                              Description
 -----------                              ------------
4.1          Amended and Restated Certificate of Incorporation of the
                 Registrant - incorporated by reference from the Registrant's Form
                 8-K/A1 filed June 17, 1999.
    4.2          Amended and Restated By-Laws of the Registrant - incorporated by
                 reference from the Registrant's Form 8-K/A1 filed June 17, 1999.
    4.3          Rights Agreement between the Registrant and American Stock
                 Transfer & Trust Company - incorporated by reference to Exhibit 4
                 to Form 8-A of the Registrant filed June 2, 1997.
    4.4          American Oncology Resources, Inc., 1993 Non-Employee Director
                 Stock Option Plan, as amended.
      5          Opinion of Mayor, Day, Caldwell & Keeton, L.L.P.
   23.1          Consent of PricewaterhouseCoopers LLP.
   23.3          Consent of Mayor, Day, Caldwell & Keeton, L.L.P. (included in
                 Exhibit 5).
     24          Powers of Attorney (included on signature page of this
                 Registration Statement).
4