OBJECTIVES The efficacy of three therapeutic protocols of transurethral microwave thermotherapy (TUMT), was compared in a study comprised of 355 patients that had been treated for benign prostatic hypertrophy (BPH) between March, 1992 and March, 1995. METHODS TUMT were performed with the Prostatron device with intravenous analgosedation and on an outpatient basis. In the first group (Protocol A), 122 patients received a standard treatment (Prostasoft 2.0/hour); the second group of 81 patients were included into Protocol B (Prostasoft 2.0/2 hours); 152 patients were treated with higher-energy in Protocol C (Prostasoft 2.5/1 hour). The number of sessions (635) performed were based on prostatic length: L < 45 mm - one session (Prostanec catheter); L < 55 mm - two sessions (additional black catheter session); L < 65 mm - three session (additional white catheter session). RESULTS All groups improved significantly for subjective symptoms (symptom score) and objective parameters (peak flow, residual urine). Comparison of the results between the three groups at 6 and 12 months showed a significantly better clinical outcome in protocol C >> B > A: Morbidity was higher in group C than in group B than in group A. CONCLUSION Our results indicate that transurethral microwave thermotherapy is a safe and effective procedure which improves objective and subjective parameters. Better outcomes were obtained with long session times (2H) and overall higher energy (2.5) input, which may be explained by the creation by cavities within the prostate, but at the cost of increased morbidity. However, TUMT can still be delivered as an anesthesia-free and outpatient non-surgical alternative treatment for BPH.