Although it is widely recognized that eating disorders primarily begin during the adolescent period, the centrality of obsessive-compulsive symptomatology and dynamisms and their relationship to adolescent conflict and development has not been generally accepted or understood. Social pressures toward conformity with the ideal of feminine thinness, which are especially influential during the adolescent period, combine with obsessive-compulsive predispositions to produce eating disorder symptoms and patterns of behavior. Obsessive preoccupation with images of food as well as ruminative calorie counting, and ritualistic behavior regarding food, use of laxatives, and vomiting, together with an underlying focus on control, undoing and other obsessive-compulsive defenses, and a sado-masochistic orientation to the body all point to an essential obsessive-compulsive disorder. The presence of dysphoric affect and the erratic success of antidepressant medication with eating disorder patients has led to a belief in an underlying affective disorder. However, careful assessment of eleven studies presenting differential diagnostic data regarding anorexia nervosa reveals that noneating related obsessive-compulsive patterns and symptoms are second overall in incidence to depressive patterns and symptoms. With critical re-evaluation of data presented, the obsessive-compulsive condition equals or supersedes the depressive one in many samples. Moreover, given the intense achievement orientation of persons with obsessive-compulsive illness, along with other psychodynamic factors, depressive symptoms could well be considered a secondary breakdown effect. If the all-pervasive obsessive-compulsive nature of eating-related symptomatology discussed here is taken into consideration, depressive symptoms must be considered either secondary or incidental. As patients with eating disorders are notoriously secretive and oftentimes misleading about their symptoms and themselves, a diagnostic assessment of such patients in intensive treatment at a long-term hospital facility was carried out. Compared with a control group randomly selected from the remainder of the hospital patient population, obsessive-compulsive manifestations of rumination, ritualistic behavior, excessive cleanliness, excessive orderliness, perfectionism, miserliness, rigidity, and scrupulousness and self-righteousness were all significantly associated with the eating disorder patient group. The current eating disorder picture, therefore, appears to be a modern form of obsessive-compulsive illness beginning during the adolescent period.