Local deep microwave hyperthermia has been introduced recently for the treatment of benign prostatic hypertrophy (BPH). We report the results of treatment in 114 patients divided into 2 groups. The first group included 83 patients with severe obstructive symptoms. Although some improvement was found in the scoring of both subjective and objective parameters, the number of patients benefiting was small, with only 28% showing improvement in both parameters. Approximately 50% reported subjective improvement but in only 25% was this significant. In 42% there was objective evidence of improvement. Prostatic volumes did not change as a result of treatment. The second group comprised 31 patients with indwelling catheters because of acute urinary retention. After treatment, 19 patients (61%) were able to dispense with the catheter. The difficulties of interpreting an open trial of treatment for BPH and assessing its impact on objective parameters and symptomatology are discussed. Our results should be regarded cautiously in view of these reservations.