Twenty patients with adenocarcinoma of the prostate underwent postradical prostatectomy adjuvant external beam megavoltage radiation therapy because of periprostatic disease in histologic evaluation of the resected specimen. Fourteen of these patients had pathologic Stage C and 6 pathologic Stage D1 disease. Treatment in most patients consisted of 5,000 rad delivered to the true pelvis. The five-year recurrence-free survival was 75 per cent for pathologic Stage C and 41 per cent for Stage D1 disease. The median time to first evidence of treatment failure was fifty months for D1 patients and has not been reached by the C group. Minor complications occurred in 85 per cent of patients and major complications in 5 per cent. In 1 patient with mild, postoperative stress incontinence total urinary incontinence developed after radiation therapy. These preliminary observations suggest a prolonged disease-free interval with an acceptable morbidity is obtained utilizing this regimen.