We administered the National Institute of Mental Health Diagnostic Interview Schedule to 41 patients with a lifetime history of anorexia nervosa (25 with and 16 without bulimia) and to 49 patients with bulimia alone. Results showed that 77% of the patients with eating disorders had a lifetime diagnosis of DSM-III major affective disorder, a rate significantly higher than that found in comparison groups composed of the first-degree relatives of probands with schizophrenia and bipolar disorder. High lifetime rates of anxiety disorders, substance use disorders, and kleptomania were also observed. By contrast, few cases of personality disorders and no cases of schizophrenia were found. These findings combine with the results of studies of family history, long-term outcome, response to biological tests, and treatment response to suggest that anorexia nervosa and bulimia may be closely related to major affective disorder.