A randomized, double blind, placebo-controlled study (placebo and Finasteride 1 or 5 mg/die) was carried out in 34 patients with benign prostatic hyperplasia (BPH). After 12 months of treatment all patients received Finasteride 5 mg/die. Follow-up ranges from 18 to 36 months. One year after treatment, patients receiving Finasteride 1 or 5 mg/die, showed significant decrease (one-way ANOVA) of serum dihydrotestosterone (-70.1% and -69.6%, respectively), serum prostate specific antigen (-50% and -50.8%, respectively) and prostate volume (-36.3% and -31.8%, respectively). Comparable modifications of such parameters were observed in the placebo group only during the second year of the study when they were shifted to Finasteride treatment (5 mg/die). No increase of serum testosterone was observed in any group. Maximum urinary flow rate increased on the average, after one year, by 2.6 and 3.6 ml/s in patients receiving Finasteride 1 and 5 mg/die, respectively; a 1.3 ml/s increase occurred in the placebo group. The total urinary symptom score (Boyarsky) decreased in all three patient groups. Results of this study show that a few months are necessary to exert a significant therapeutic effect. The drug is well tolerated and does not decrease the patient's sexual activity. Finasteride certainly opens new perspectives in the treatment of BPH.