Objective: Inpatient treatment effectively increases body weight and decreases eating disorder symptoms in adolescents with anorexia nervosa (AN). However, there is a high risk of relapse within the first year after discharge, which calls for investigating long-term treatment success and its moderators. Method: Female adolescent inpatients with AN (N ¼ 142) were assessed, of which 85% participated at 1-year follow-up. Dependent variables were body mass index percentiles, eating disorder symptoms, depressive symptoms, compulsive exercise and life satisfaction. Results: On average, body weight increased and eating disorder symptoms and depressive symptoms decreased from admission to discharge and remained stable at follow-up. Compulsive exercise decreased and life satisfaction increased from admission to discharge and even improved further at follow-up. Age, duration of illness, previous inpatient treatments, length of stay and readmission after discharge moderated changes in several outcome variables. Conclusions: This study confirms the high effectiveness of inpatient treatment for adolescents with AN and demonstrates that treatment effects remain stable or even improve further within the first year after discharge. However, subgroups of patients (e.g., those with an older age, longer duration of illness, and previous inpatient treatments) require special attention during inpatient treatment and aftercare to prevent relapse. K E Y W O R D S adolescents, anorexia nervosa, inpatient treatment, moderators, treatment outcome 1 | INTRODUCTION AND AIMS Anorexia nervosa (AN) is an eating disorder marked by restriction of energy intake-which leads to a significantly low body weight-intense fear of gaining weight and body image disturbance (American Psychiatric Association, 2013). Although AN can occur at any age, the highest incidence rates can be found in adolescence (Zipfel, Giel,

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