This research project aims to characterize a naturalistic cohort of children and adolescents with eating disorders in terms of biological, psychological and psychopathological features. Further, the project will examine the effectiveness of treatment, the determinants of treatment outcome and the course of treatment response for children and adolescents with eating disorders (ED), treated in a generic specialist child and adolescent mental health service. The first choice of treatment is outpatient family-based treatment (FBT), which has documented effect for anorexia nervosa and bulimia nervosa. However, a subgroup of young persons with eating disorders does not respond sufficiently to this treatment, and evidence concerning effective treatment for children and adolescents with atypical eating disorders is still lacking. Further, treatment effectiveness for children and adolescents in a Danish naturalistic setting has never been examined.