One hundred and forty-four patients with symptomatic benign prostatic hyperplasia were treated by transurethral microwave thermotherapy between January and December 1991. Before entering the study, all patients had a Boyarsky symptom score >8, peak flow rate < 15 ml/s and postvoiding residual urine <200 ml. Transurethral thermotherapy with the Prostatron (Technomed) was carried out as a single session (60 min) without any analgesia or sedation. Acute urinary retention occurred in 19.4% of the patients after treatment requiring catheterization for 2-3 weeks; morbidity rate was 5.5%. Six months after treatment, Boyarsky symptom score decreased from 11.73 ± 4.97 to 4.40 ± 3.21 (mean values ± SD); peak flow rate increased on average from 8.97 ± 4.18 to 13.07 ± 4.87 ml/s and postvoiding residual urine decreased from 135 ± 17.9 to 63 ± 34.7 ml. Slight further improvement was shown, in a few patients, at the 1-year follow-up visit.