Anorexia nervosa (AN) and bulimia nervosa (BN) are disorders characterized by abnormal patterns of weight regulation and eating behavior and by disturbances in attitudes and perceptions toward weight and body shape. Etiologic research has indicated substantial genetic influence on these disorders, suggesting significant biological contributions to their development. Obsessional, perfectionistic, and anxious personality styles may be premorbid traits that contribute to this pathogenesis. Studies of neuroendocrine, neuropeptide, and neurotransmitter functioning in patients with AN and BN indicate that disturbances of these systems may contribute to the maintenance as well as the etiology of these sometimes fatal disorders. The efficacy of psychological treatments and pharmacotherapy has been more clearly established for BN than for AN.