Skills trainings for caregivers of patients with anorexia nervosa (AN) have been proven to be effective in improving caregiver skills and reducing caregivers' psychopathology. The effects on patients, especially adolescents, are largely unknown. The aim of this study was to evaluate the effectiveness of a caregivers' skills training program (Supporting Carers of Children and Adolescents with Eating Disorders in Austria, SUCCEAT, workshop or online version) on adolescents with AN delivered as workshops (WS) or online (ONL). Outcomes are Body-Mass-Index (BMI) percentile, eating psychopathology (Eating Disorder Examination, EDE), attitudinal and behavioural dimensions of eating disorders (Eating Disorder Inventory-2), motivation to change (AN Stages of Change Questionnaire), emotional and behavioural problems (Youth Self-Report) and quality of life (KINDL). All outcome variables significantly improved across both SUCCEAT groups (WS and ONL) and were sustained at 12-month follow-up. The online and workshop delivery of SUCCEAT were equally effective. Most effect sizes were in the medium-to-high range. Full or partial remission was observed in 72% (WS) and 87% (ONL) of patients. Caregiver skills trainings, either delivered as workshops or online modules, are highly recommended to complement treatment as usual.