Transurethral microwave thermotherapy of the prostate was used to treat men with symptomatic benign prostatic hypertrophy. Three treatment protocols delivering increasing thermal doses (Prostasoft T-A > Prostasoft II > Prostasoft I) were evaluated. The results show a dose-dependent response. Histological changes induced by microwave heating were dependent on the temperature achieved in the tissue. Thermocoagulation is obtained above 45 degrees C and thermoablation above 60 degrees C. Using Prostasoft II in a long-term follow-up study, the Madsen symptom score decreased by 66% and peak flow rates increased by 41% over a period of more than 18 months. Using Prostasoft T-A (thermoablation) in 28 patients, a cavity was obtained inside the prostate without major complication. The symptoms and obstruction caused by benign prostatic hypertrophy can be treated by transurethral thermotherapy in a single, anesthesia-free 1-hour session on an ambulatory basis.