The internist plays a critical role in the care of eating disorder patients, especially in the management of the life-threatening medical complications of these conditions. In anorexia nervosa, the immediate danger is related to the effects of voluntary starvation, including hypophosphatemia, bone marrow failure, cardiac decompensation, and shock. Patients with bulimia nervosa more often experience severe fluid and electrolyte abnormalities resulting in hypovolemia, secondary hyperaldosteronism, depletion of total body potassium, and cardiac arrhythmias. Immediate management of medical complication and correction of nutritional deficits are necessary before patients can benefit from psychotherapy. The need for continued involvement of the internist in the ongoing care of the eating disorder patient is stressed. The high mortality and the likelihood of chronicity without early intervention underscore the need for early recognition and skilled management of eating disorders.