PURPOSE To test the hypothesis that increasing radiation dose delivered to men with early-stage prostate cancer improves clinical outcomes. PATIENTS AND METHODS Men with T1b-T2b prostate cancer and prostate-specific antigen /= 3 genitourinary toxicity, and 1% of patients in the high-dose arm experienced late grade >/= 3 GI toxicity. CONCLUSION This randomized controlled trial shows superior long-term cancer control for men with localized prostate cancer receiving high-dose versus conventional-dose radiation. This was achieved without an increase in grade >/= 3 late urinary or rectal morbidity.