Transurethral radiofrequency thermotherapy for symptomatic benign prostatic hyperplasia was performed in 50 selected patients, using the THERMEX II device. High surgical risk patients were included, among them 13 previously catheterized ones, because of unresolved retention for more than 6 months. The treatment consisted of a three-hour single session at 47 degrees C. Follow-up studies were carried out at 1, 3, 6 and 12 months using Madsen score, maximum flow rate, residual urine volume determinations and prostate bulk measurement by transrectal ultrasound. Subjective and objective improvement (of more than two parameters) was noticed in 62% of the patients. Prostatic volume did not change. In the retention group 54% of the patients remained free of catheter. Postoperative histology in 8 cases that failed to respond, revealed focal haemorrhagic and necrotic changes in periurethral glandular tissue. This is a promising method for selected high risk patients that achieves reasonable but not comparable results to TURP and requires further investigation in larger patient groups with BPH.