Saw palmetto for benign prostatic hyperplasia has reached a widespread use in the United States of America. Phytotherapeutic efficacy of saw palmetto has been questioned although prior randomized controlled trials showed improvements in the symptoms of benign prostatic hyperplasia or in urinary flow rates. This is a randomized, placebo controlled double-blind trial which included 225 men over the age of 49 who had moderate to severe symptoms of benign prostatic hyperplasia. These men were randomized to take either 160 mg twice a day saw palmetto or placebo for a period of one year. Changes in the American Urological Association Symptom Index scores and maximal urinary flow rates were taken as primary outcome measures, whereas changes in prostate size, postvoiding residual urinary volume, quality of life, laboratory values and the incidence of encountered adverse effects were evaluated as secondary outcome measures. At the end of one year use the differences between treatment and placebo groups were significant neither in terms of primary (95% confidence interval) nor secondary outcome measures. In this study saw palmetto failed to improve symptoms or other objective measures of benign prostatic hyperplasia.