Interventions for main carers of adult patients with anorexia nervosa (AN) can reduce the caregiving burden and increase caregiver skills. However, the effectiveness and feasibility for carers of adolescent patients, the optimal form of the intervention and long-term outcomes are largely unknown. We evaluated the efficacy and feasibility of the "Supporting Carers of Children and Adolescents with Eating Disorders in Austria" (SUCCEAT) workshop vs. online intervention. Main caregivers (parents) of adolescent patients with AN were randomly allocated to a workshop ( n = 50) or online version ( n = 50). Participants were compared to a non-randomised comparison group ( n = 49) receiving multi-family or systemic family therapy. Primary (General Health Questionnaire) and secondary outcomes were obtained at baseline, three-month and 12-month follow-up. Adherence was high for workshop and online participants (6.2 and 6.7 sessions completed out of 8). Intention-to-treat analyses revealed significant pre-post reductions in the primary outcome for the workshop (d = 0.87 (95%conficence interval (CI): 0.48; 1.26)) and online (d = 0.65 (95%CI: 0.31; 0.98)) intervention that were sustained at the 12-month follow-up. There was no significant group difference ( p = 0.473). Parental psychopathology and burden decreased and caregiver skills increased in all groups; the improvement of caregiver skills was significantly higher in SUCCEAT participants than in the comparison group. Online interventions for parents of adolescents with AN were equally effective as workshops. The improvements remained stable over time.