It is important that treatment decisions be based upon scientific data, as opposed to anecdotal experience and expert opinion. The goal of this article is to provide an update on phase III clinical trials in localized and locoregional prostate cancer. Studies comparing surgery and observation for localized disease are reviewed, as are studies comparing various forms of radiotherapy. The effectiveness of certain neoadjuvant and adjuvant therapies is also addressed. Although there are numerous phase III studies ongoing in these areas, there are still large gaps in our understanding of the treatment of localized disease, and additional clinical trials are needed.