A 39-year-old man with Prader-Willi syndrome presents for evaluation of uncontrolled weight loss. Past history was significant for gastric bypass and prior episodes of intentional dieting. Family history was significant for an alcoholic father and two siblings with anorexia nervosa. The patient was unconcerned about his weight loss despite cachexia and did not want to stop dieting. This presentation of a restrictive eating pattern in a man with a syndrome usually associated with compulsive hyperphagia is the first known report © 2001 by John Wiley & Sons, Inc. Int J Eat Disord 30: 231–233, 2001.