Objectives. To summarize the 6-year clinical trial data with finasteride. Benign prostatic hyperplasia is a chronic and progressive disease and therefore assessment of long-term safety and efficacy is important. Methods. The North American and International Phase III Finasteride trials enrolled symptomatic men with enlarged prostate glands. The initial 1-year placebo-controlled study was followed by a 5-year open-label extension. In total, 6-year finasteride data were available in 487 patients originally randomized to finasteride, and 5-year data were available on 238 patients originally randomized to placebo. Results. After 6 years of treatment with finasteride 5 mg, the mean quasi-American Urological Association Symptom Score improved by 4.0 points, the median prostate volume decreased by 24%, and the mean maximal urinary flow rate increased by 2.9 mL/s (P <0.001 for all parameters). Long-term finasteride treatment was well tolerated, with a low incidence of drug-related sexual adverse events occurring during the first year and even fewer occurrences during the 5-year open extension. Conclusions. Treatment with finasteride leads to durable improvement in urinary tract symptoms, flow rate, and prostate volume, with no increase in the prevalence of drug-related adverse events over time.