Approximately 25% of patients experience recurrent disease after radical prostatectomy. Most frequently, the only evidence of a relapse is a rising PSA level without clinical evidence. Without further treatment the natural history of PSA progression results in local recurrence or distant metastasis of prostate cancer. Since a proportion of these biochemical failures relate to a local recurrence, radiotherapy offers a potential curative approach. Up to now, no randomized studies are available. Therefore any decision can only be based on prospective observation studies or retrospective data. The data available indicate that optimal results can be obtained in patients with PSA levels below 1-2 ng/ml or even lower, a documented R1 resection, and a PSA doubling time>10 months. Doses of 64-66 Gy seem to be required for adequate control. Side effects are generally well acceptable and importantly no adverse effects on urinary continence have been documented. Taken together, radiotherapy is the only treatment option with curative potential in situations where a local failure is highly likely.