We retrospectively evaluated the subjective and objective treatment results of transurethral microwave thermotherapy (TUMT) for benign prostatic hyperplasia (BPH) and explored the difference in effectiveness between 30- and 60-min single treatments. From June 1997 through March 2003, 58 men with BPH underwent TUMT using the Targis device. Twenty-seven and 31 patients each received a single treatment of 60 or 30 min, respectively. Evaluations after treatment included a clinical determination of the International Prostate Symptom Score, urodynamic assessments by peak flow rate, and magnetic resonance imaging (MRI). In the 60-min treatment, the symptom score improved significantly, from 17.9 to 9.5 after 2 months. Similarly, there was a significant improvement in peak flow rate, from 6.7 to 11.2 ml/sec after 2 months. In the 30-min treatment, the symptom score also improved significantly, from 18.4 to 13.4 after 2 weeks. Similarly, there was a significant improvement in the peak flow rate, from 6.4 to 11.7 ml/sec after 1 month. MRI imaging showed necrosis of the prostate gland 2 weeks after either treatment. These results demonstrated that both the 60-min and the 30-min treatments were effective for patients with BPH. Moreover, the 30-min treatment led to quicker improvement than the 60-min treatment. Thus, a 30-min TUMT protocol is considered recommendable for this treatment.