Benign prostatic hyperplasia (BPH) is a disease diagnosed by the presence of prostatic enlargement and lower-tract urinary obstruction. Finasteride (Proscar), is a potent and specific inhibitor of 5alpha-reductase, which inhibits the conversion of testosterone (T) to dihydrotestosterone (DHT) an important promoter of prostatic growth. It has provided a new therapeutic alternative for the treatment of BPH. The safety and efficacy of finasteride in the treatment of symptomatic BPH have been demonstrated by two multi-center placebo-controlled studies. After 12 months of treatment with 5 mg finasteride daily, prostate volume, DHT and prostate-specific antigen (PSA) levels were reduced and maximum urinary flow rates and symptom scores were improved. Finasteride was well-tolerated. Upon completion of the controlled studies, patients were eligible to enter an open-label extension study in which all patients received 5 mg finasteride. Approximately half of the 543 patients randomized to the 5 mg finasteride group in the controlled studies have now been treated with 5 mg finasteride continuously for 3 years. The data provided by this group of patients on the long-term safety and efficacy of finasteride in the treatment of symptomatic BPH are reviewed.