The Saw palmetto for Treatment of Enlarged Prostates study was a randomized clinical trial performed among 225 men with moderate-to-severe symptoms of benign prostatic hyperplasia, comparing a standardized extract of the saw palmetto berry (160mg twice daily) with a placebo over a 1-year period. No evidence for serious side effects or dangers of saw palmetto was observed in this 12 month long clinical trial. For details, see http://www.raysahelian.com/saw.html 
My comments: This is reassuring since saw palmetto is a supplement used by men for many months and years. I hope in a few years we can have results of a longer study, such as five years.