The aim of this prospective longitudinal study was to examine the course of adolescent anorexia nervosa and obsessive-compulsive disorder (OCD) (fulfilling DSM-III-R criteria) to compare psychiatric comorbidity and personality disorders of both groups. Because anorexia nervosa patients are mainly female, we compared them only with female OCD patients. Ten years after discharge the whole sample (32 female patients; 100%) of a group of 39 (32 female; 7 male) anorexia nervosa patients could be reexamined personally. 25 (61%) female patients of a group of 116 patients (41 female; 75 male) with obsessive-compulsive disorder were also reexamined. The anorexia nervosa patients were interviewed using the Structured Interview for Anorexia and Bulimia nervosa (SIAB [39]) to assess eating disorder symptomatology. To examine comorbid psychiatric disorders we used the Composite International Diagnostic Interview, WHO [44] and SCID-II [45] for personality disorders. One fourth of the patients with anorexia nervosa (AN) and 20% of the patients with obsessive-compulsive disorder had a personality disorder according to DSM-III-R. Most of them were "Cluster C"-personality disorders (AN: 28%; OCD: 20%). In the group of the female OCD patients 8% schizoid, 4% schizotype and 12% paranoid personality disorders were observed. The most prevalent psychiatric disorders were anxiety (AN: 28%; OCD: 20%) and affective disorders (AN: 16%; OCD: 16%). Our results support the view that in the course of anorexia nervosa and in obsessive-compulsive disorder there is a high prevalence of psychiatric comorbidity and "Cluster C"-personality disorders according to DSM-III-R. These results might confirm a model of a high vulnerability of the serotonergic neurotransmitter system in patients with anorexia nervosa or OCD.