Purpose: We performed a retrospective analysis to assess the durability of benefit derived from irradiation after prostatectomy for pT3NO disease, and the possibility of cure. Methods and Materials: We studied 88 patients who were irradiated after prostatectomy and had available prostate specific antigen (PSA) data, no known nodal or metastatic disease, no hormonal treatment, and follow-up of at least 12 months from surgery, Forty patients received adjuvant therapy for a high risk of local failure with undetectable PSA, Forty-eight patients received salvage therapy for elevated PSA levels, Mean follow up was 44 months from date of surgery and 31 months from irradiation, Biochemical failure was strictly defined as a confirmed rise in PSA of >10%, or as the ability to detect a previously undetectable PSA value. Results: After salvage irradiation, 69% of patients attained an undetectable PSA, Eighty-eight percent of adjuvant patients were biochemically and clinically free of disease (bNED) at 3 years from prostatectomy, Sixty-eight percent of those receiving salvage irradiation were bNED 3 years after surgery, On univariate analysis, treatment group (adjuvant or salvage), pre-operative PSA, and the status of seminal vesicles were significant prognostic factors, The extent of PSA elevation in the salvage group was also significant, We did not demonstrate a significant difference between those salvage patients referred for persistently elevated PSA as compared to those with a late rise in PSA, On multivariate analysis, the only significant predictor of outcome was treatment group, with adjuvant irradiation having better outcome than salvage. Conclusion: More than two-thirds of this group of patients remain biochemically disease free at 3 years following irradiation, attesting to a number of potential cures, For patients with stage pT3NO prostate cancer following radical prostatectomy, our data support the use of either routine postoperative adjuvant irradiation or close PSA follow-up with early salvage treatment. (C) 1997 Elsevier Science Inc.