In adolescents, anorexia nervosa severely affects physical, emotional, and social development. Despite the seriousness and prevalence of adolescent anorexia nervosa, few studies have focused on the effectiveness of various types of psychotherapy treatment. Family-based therapy may be an effective approach to treating adolescent anorexia nervosa. This study will compare the effectiveness of family-based therapy versus ego-oriented individual psychotherapy for the treatment of adolescent anorexia nervosa. Simultaneously, it will examine potential predictors, mediators, and moderators of weight gain, psychological concerns about weight and shape, and changes in family functioning.