Prostate cancer is the most common cancer in men and radical prostatectomy is the most frequent treatment for this disease. Unfortunately, approximately 40% of patients will develop recurrence after surgery, requiring additional salvage radiation. Salvage radiation after recurrence is successful in less than half of these men and most of those die from their disease. Measures to prevent recurrence are an important research priority for prostate cancer patients and their families. Hormonal therapy (androgen deprivation therapy; ADT) is routinely used to treat patients with metastases, but few clinical trials have examined if adjuvant ADT after surgery will prevent cancer recurrence. We aim to address this research oversight and test the hypothesis that for men at high risk of cancer recurrence, 1 year of ADT immediately after surgery will be safe and will significantly improve cancer outcomes.