Anorexia Nervosa (AN) is a key target for E-Health programs considering the many barriers hindering patients' access to care and the disorder's severity. Although these programs have become more common and effective, they often have low adherence, especially among youth. This can hinder their implementation and effectiveness in real-world settings. User experience partly overlaps with the acceptability field and may provide insight into factors affecting adherence and adoption of E-Health programs. This study aimed to explore early acceptability and user experience of a companion app prototype for adolescents with AN using user-centered design methods.