Four patients who developed anorexia nervosa after the onset of diabetes mellitus are described. It is postulated that the co-occurrence of the two conditions was not coincidental, but that each contributed to the development of the other. The nature and treatment of diabetes offer numerous opportunities for the anorexic patient to lose weight by a variety of dangerous maneuvers, including adjustment of the insulin dose, failure to inject insulin, secret vomiting, and failure to provide urine samples. Treatment of patients with both conditions is a therapeutic challenge to the psychiatrist and diabetologist. A behavior management program combined with psychotherapy is most often effective.