Definitive radiation therapy was administered to 577 patients with histologically confirmed carcinoma of the prostate localized to the pelvis. Results of therapy and prognostic factors are evaluated and compared with other reports. All patients were followed for a minimum of 3 years, the median period of observation is 6.5 years. The disease-free survival in stages A2 and B was 78% at 5 years and 60% at 10 years; in stage C, 60% at 5 years and 36% at 10 years. The overall actuarial survival in stage B patients was 76% at 5 years and 58% at 10 years, which is similar to the life expectancy of a comparable cohort of normal males. In stage C, the actuarial survival was 65% at 5 years and 38% at 10 years, approximately 15% below the normal life expectancy for a similar cohort. Histological differentiation of the tumor had a significant impact on survival, poorly differentiated tumors showing 20% lower survival rates, most likely related to a higher incidence of distant metastases. Age was not found to be a significant prognostic factor in patients with stage B tumors; however, in stage C, the 5-year disease-free survival was 43% in patients younger than 60 and 53% in those older than 60 years (p = 0.04). In stage B, patients who had control of the pelvic tumor exhibited a 80% actuarial 5-year survival and 60% at 10 years. This compares with an actuarial survival of 30% at 5 and 10 years when there was evidence of pelvic recurrence alone or combined with distant metastases. In stage C patients with pelvic tumor control, actuarial survival was 81% at 5 years and 50% at 10 years, in comparison with 20% 5-year and 10% 10-year survival when pelvic recurrence or distant metastases or a combination of both occurred. The method of diagnosis [transurethral resection of the prostate (TURP) versus needle biopsy] did not appear to be a major prognostic factor of survival or patterns of failure, except in patients with stage C moderately differentiated tumors. The interpretation of the lymphangiogram (normal, suspicious or abnormal) did not correlate with survival or tumor control. The pathologic status of the lymph nodes established at lymphadenectomy did not appear to relate to survival for patients with stage B disease.(ABSTRACT TRUNCATED AT 400 WORDS)