Objective To evaluate retrospectively the potential influence of disease-related factors and transurethral resection of the prostate (TURF) on the sexual function of patients who had undergone curative radiotherapy for prostate cancer. Patients and methods The study comprised 104 patients (median age 69.5 years, range 49-81) who had been treated with curative radiotherapy and no first-line hormones: 16, 52, 33 and three patients had T1, T2, T3 and T4 tumours, respectively. TURF was performed in 73 patients before RT, and needle biopsy alone in 31 patients. They were interviewed about their past and present sexual lives using a questionnaire designed to evaluate the potency of the patients at age 45 years, at 1 year before the diagnosis of the disease, before radiotherapy (after TURF or needle biopsy) and at the last follow-up. Information concerning associated diseases, routine medication and the weight of the resected material was also collected. Results Before diagnosis, 20 patients had no erections while 84 were potent. Of the 60 potent patients undergoing a TURF, 31 (51%) indicated complete impotence immediately thereafter. There was no statistical difference between impotent and potent patients after TURF in age, associated diseases, medical treatment and the weight of the resected material. Conclusion TURF may lead to impotence in a significant proportion of patients. As TURF is an important component of 'conservative' treatment approaches, its potential sexual morbidity should be taken into consideration in the comparative risk-benefit analysis of different therapeutic strategies.