Allylestrenol at the daily dose of 50 mg was administered to 45 patients with benign prostatic hypertrophy. The treatment was performed for more than 12 weeks in 40 patients, and improvements, marked and moderate, were observed in 22 patients (55%) in the overall judgement. As side effects of this drug, decrease of potency was observed in 3 cases, decrease of libido in 1 case, pigmentation on breasts in 2 cases, palpitation in 2 cases, short breath in 1 case, and gastrointestinal symptoms in 1 case. However, these side effects were not serious. Our trial suggests that the treatment of benign prostatic hypertrophy with allylestrenol can be useful in urological clinics.