Personality disorders and axis I disorders show complex patterns of comorbidity. There are a considerable number of studies examining the comorbidity of eating disorders. Approximately 50% of patients with eating disorders (anorexia nervosa, bulimia nervosa or binge eating disorder) suffer from cluster C or cluster B personality disorders. The absence or presence of comorbidity with a personality disorder seems to be a major determinant of the degree of impairment of psychosocial function and the number of further comorbid axis I disorders. Patients with cluster B seem to be more severely impaired than patients with cluster C personality disorder. The personality disorder does not predict the response to interventions targeted at eating disorder specific behaviors. There are very few studies examining the comorbidity of specific personality disorders and eating disorders. Precise data are only available for borderline personality disorders. Approximately 50 to 70% of these patients suffer from a specific eating disorder. The presence of an eating disorder is associated with decreased social function and increased comorbidity with other axis I disorders, in particular depressive disorders. Open questions relate to the hierarchy of therapeutic interventions in patients with high comorbidity. Potential algorithms for treatment planning are presented.