Finasteride, a 5-alpha-reductase inhibitor, dramatically suppresses the production of dihydrotestosterone in men; thus, attention has turned to this agent for the treatment of benign prostatic hyperplasia (BPH). A number of randomized clinical trials have studied finasteride's effects on prostate size, BPH symptoms, flow rate, and prostate-specific antigen (PSA) level. Although the decrease in symptoms with finasteride therapy has been modest compared with more invasive treatments, its use has resulted in sustained reductions in prostatic volume and PSA level with minimal adverse effects. Fewer surgeries for BPH, as well as a decreased incidence of acute urinary retention, have also been seen with finasteride therapy. More research is needed to maximize the effectiveness of such medical therapy for BPH.