Inclusion Criteria

1. Adenocarcinoma of prostatic origin histologically-confirmed within 180 days of the randomization date.
2. Zubrod Performance Status 0-1 (Appendix II).
3. Prostatic biopsy tumor grading by the Gleason Score classification (Appendix VI) is mandatory prior to randomization.
4. Patients at intermediate risk for disease relapse as determined by any of the following combinations of factors (NOTE: tumor found in one or both lobes on biopsy, but not palpable, will not alter T stage):

* Clinical stage T1b-4, Gleason score 2-6, and prostate-specific antigen \>10 but ≤ 100.
* Clinical stage T1b-4, Gleason score 7, and prostate-specific antigen \< 20.
* Clinical stage T1b-1c, Gleason score 8-10, and prostate-specific antigen \<20.
5. Clinically negative (N0) lymph nodes (LN) as established by imaging (pelvic ± abdominal CT, MRI or LAG), or negative LN by nodal sampling or dissection (laparoscopy or laparotomy). Patients with radiologic (e.g., CT, MRI or LAG) or radioimmunoscintigraphy (i.e., ProstaScint™) findings suggestive of regional nodal involvement are eligible if cytologic (e.g., needle aspiration) or histologic (e.g., surgical sampling) evaluation shows no evidence of a neoplastic process (i.e., prostatic or non-prostatic malignancy). Patients with equivocal radiologic findings (maximum nodal size ≤ 1.5 cm) are eligible.
6. No distant (M0) metastases. Patients with radionuclide imaging (e.g., bone scintigraphy, ProstaScint™) findings suggestive, but not diagnostic of metastatic disease are eligible if radiologic (e.g., standard or tomographic radiography, or CT/MRI) imaging does not confirm metastatic disease.
7. Pretherapy serum (total) prostate-specific antigen value performed with a Federal Drug Administration approved assay method, e.g. Abbott, Hybritech, etc.
8. Treatment must begin within 6 weeks after randomization.
9. Alanine aminotransferase (ALT) must be within 2 x upper normal limit.
10. Patients must sign a study-specific informed consent form (Appendix I) prior to randomization.

Exclusion Criteria

1. Patients at high risk for disease relapse as determined by either:

* Prostate-specific antigen ≥ 20 and Gleason score ≥ 7 (any T stage).
* Clinical stage ≥T2 and Gleason score ≥ 8 (any prostate-specific antigen).
2. Patients at low risk for disease relapse as determined by:

• Clinical stage ≤T2, Gleason score ≤ 6, and prostate-specific antigen ≤ 10.
3. Clinical stage Tx, T0, or T1a.
4. Histologic or radiologic evidence of tumor involvement of regional lymph nodes (N1) or the presence of metastatic disease (M1).
5. Pretherapy serum prostate-specific antigen level \> 100.
6. Co-morbid medical illness which in the opinion of the investigator is expected to result in a life expectancy of \<10 years.
7. Any of the following prior therapies:

* Pelvic external beam radiation therapy.
* Radionuclide prostate brachytherapy.
* Prostatectomy or prostatic cryosurgery.
* Prior bilateral orchiectomy.
* Prior androgen suppression therapy; however, patients begun on LHRH agonist therapy remain eligible if (1) LHRH agonists were started no more than 30 days before randomization, and (2) Casodex or Eulexin was (or will be) started no more than 14 days before or after the date that the LHRH agonist injection was given. Any finasteride therapy administered for prostatic hypertrophy must be discontinued.
* Chemotherapy for prostatic carcinoma.
8. Previous or concomitant invasive cancer, other than localized basal cell or squamous cell skin carcinoma (AJCC Stage 0-II), unless continually disease free for at least 5 years.
9. Major medical or psychiatric illness which, in the opinion of the investigator, would prevent completion of treatment or would interfere with follow-up.
10. The patient's participation in another medical research study that involves prostate cancer treatment.