ABSTRACT Objective When a young person has an eating disorder (ED), the entire family, including siblings, is affected. Despite recommendations in clinical guidelines and treatment manuals to involve and support siblings, little is known about how this is enacted and documented in practice. The aims of this study were: (1) to audit documentation of sibling information and involvement in child and adolescent ED services and its alignment with clinical guidelines, and (2) to explore healthcare professionals' perspectives on sibling involvement. Method A mixed‐methods design was used. Clinical records of 102 young people receiving ED treatment were reviewed, and data were extracted using a data collection tool. Data were analyzed descriptively. A focus group discussion was conducted with 14 healthcare professionals. Data were analyzed qualitatively, applying thematic analysis. Results Eighty‐six of 102 patients (84%) had siblings ( n  = 160 siblings across the sample). Attendance in sessions was documented for 20 of the 160 siblings (13%) across 19 of the 102 patients (19%). Across all records, one record documented sibling perspective and support offered. Qualitative analysis of the focus group identified six themes. Sibling involvement was seen as overwhelming, constrained by workload, privacy concerns, and lack of appropriate resources, and conceptualization of involvement was limited to session attendance. Perceived benefits included enhanced systemic insight and improved family communication. Discussion In this study, documentation of sibling involvement in child and adolescent ED care was limited. Clearer documentation practices, broader conceptualizations of sibling involvement, and further research are needed to ensure siblings receive appropriate support.