Multi-family therapy (MFT) is a recommended treatment for adolescent anorexia nervosa internationally. Despite recent significant advances in single-family therapy, the evidence base for MFT remains relatively small. Several individual and family factors have been associated with poorer outcomes in single-family therapy, many of which may be addressed or ameliorated by MFT if delivered early in treatment. This trial aims to determine the feasibility and acceptability of adding a five-day multi-family therapy group to the early stages of family therapy for anorexia nervosa. Secondary objectives are to explore effect size changes in key individual and family factors across treatment.