Patients with adenocarcinoma of the prostate with positive surgical margins and/or seminal vesicle invasion after radical prostatectomy (RP) have a high risk of local recurrence or distant spread of disease. Several investigators reported increased local control rates following adjuvant radiotherapy (RT). However, it is unclear whether this procedure, with or without hormonal therapy (HT), improves the outcome. From 1975 to 1987, 56 patients with adenocarcinoma of the prostate underwent adjuvant RT following RP (pathological stage C1, n = 19; stage C2, n = 17; stage D1, n = 20). In 27 of 56 patients an additional immediate orchiectomy was performed. 48 patients received 4000-5000 cGy to the pelvic lymphatics, including the prostatic fossa, followed by a boost to the prostatic fossa to complete 6400-7000 cGy, whereas 8 patients were treated to the prostatic fossa only. With a median follow-up of 89 months, the overall survival rate of patients with stages C1, C2 and D1 did not differ significantly (10-year overall survival rate 84, 74 and 71, respectively). The local control rate for 5- and 10-years was 96 and 90%, respectively. A significant advantage in overall survival (5- and 10-year rate: 92 versus 93% and 92 versus 63%; P < 0.05, respectively) and clinical disease-free survival (5- and 10-year rate: 92 versus 72% and 92 versus 49%; P < 0.05, respectively) was seen in 27 patients with orchiectomy compared with 29 patients without HT. A total of 15 patients (26%) developed at least one form of late toxicity, in most cases a mild proctitis, cystitis, or penile or leg oedema. However, 6 patients (11%) had severe grade 3 or 4 side-effects that necessitated a cystectomy in 2 cases as well as a colostomy in 2 cases. In all patients with grade 3 or 4 side-effects, 70 Gy as a tumour-encompassing isodose were applied. Adjuvant RT, following RP in stage C and D1 prostate cancer with positive surgical margins and/or seminal vesicle invasion increases local control. Whether immediate HT influences the outcome, as seen in this study, should be proven in prospective clinical trials.