Biochemical relapse after radical prostatectomy is not exceptional, ranging from 10 to 40% in the literature. To prevent this biochemical failure, adjuvant radiotherapy was proposed to patients with a high risk of relapse. No phase III trial has actually validated this attitude. Best indications for adjuvant irradiation seem to be patients with an extensive extracapsular extension or multiple positive margins. Historical comparisons seems to confer, in these case, a benefit in biochemical control for adjuvant irradiation versus observation. Others authors prefer immediate post-operative irradiation, a delayed treatment, when biochemical relapse has occurred. This attitude has spared some patients irradiation useless. This salvage irradiation lowered the PSA level in 40 to 70% of the cases, but long-term efficiency is obtained only in the case of a low value of the PSA before irradiation. Delayed radiotherapy is, therefore, justified only if a close follow-up is performed, with repeated dosage of PSA. Whatever the case, it is important to differentiate between local and distant relapse: patients with positive nodes at the time of surgery are most likely at risk of distant relapse. It seems that patients with seminal vesicles involvement are also at high risk for distant relapse, but this must be confirmed.