This study is open to men who have prostate cancer and report feeling fatigue. We will examine the impact of psychostimulant treatment on depressive symptom severity, neuropsychological test performance, and overall quality of life, as well as compare the frequency and severity of treatment associated adverse side effects. We will be conducting a six-week, randomized, double-blind, placebo-controlled, parallel design trial, evaluating the relative benefits and risks of methylphenidate, (a psychostimulant medication). Medication will be given in once or twice daily dosages (at 8 am and noon) and titrated by one capsule every 2-3 days as needed to treat fatigue and as tolerated. Patients will be examined regularly for safety. We will monitor vital signs and response to the medication. This study will be the first of its kind to evaluate a pharmacologic intervention for fatigue in cancer patients that utilizes a novel psychotropic agent (psychostimulant), and assesses outcome with measures of fatigue, as well as side effects, psychological distress, depression and overall quality of life.