A case of post renal acute renal failure secondary to radiation therapy for prostate cancer is described. Severe bladder inflammatory reaction, leading to bilateral ureteric obstruction, occurred after a moderate dose of radiotherapy (6400 cGy in 35 fractions). At a follow-up time of 8 years, the patient has fully recovered and remains disease-free. To our knowledge, this complication has never been described previously. Given the thrust in prostate cancer treatment toward dose escalation this complication could become more frequent.