Chronic nonbacterial prostatitis is an ill-understood and difficult-to-diagnose disease. Symptoms of chronic nonbacterial prostatitis are similar to those of chronic prostatitis and include low back pain, frequency, dysuria, perineal discomfort, and painful ejaculation. In view of uncertainty about etiology, treatment of chronic nonbacterial prostatitis remains speculative. Most treatment is aimed at relieving symptoms and not at curing the disease. Because of the troublesome nature of chronic nonbacterial prostatitis and the poor results obtained from traditional treatment methods, a new modality of transurethral microwave hyperthermia was investigated. Six patients were treated from January 1994 through June 1995 by use of transurethral microwave hyperthermia. These men were treated four times during a 2-week period. Their average symptom score decrease was 74.9% and was associated with minimal morbidity. Based on this result, it is concluded that transurethral microwave hyperthermia is a safe and effective treatment modality for chronic nonbacterial prostatitis.