BackgroundEating disorders (ED) are severe psychiatric conditions, characterized by decreased quality of life and high mortality. However, only a minority of patients with ED seek care and very few receive treatment. Internet-delivered cognitive behavioral therapy (ICBT) has the potential to increase access to evidence-based treatments.AimsThe aims of the present study were to (1) develop and evaluate the usability of an Internet-delivered guided self-help treatment based on Enhanced Cognitive Behavioral Therapy (ICBT-E) for patients with full or subthreshold bulimia nervosa (BN) or binge eating disorder (BED) with a user centered design process, and (2) to evaluate its feasibility and preliminary outcome in a clinical environment.MethodThe study was undertaken in two stages. In Stage I, a user-centered design approach was applied with iterative phases of prototype development and evaluation. Participants were eight clinicians and 30 individuals with current or previous history of ED. In Stage II, 41 patients with full or subthreshold BN or BED were recruited to a single-group open trial to evaluate the feasibility and preliminary outcome of ICBT-E. Primary outcome variables were diagnostic status and self-rated ED symptoms.ResultsThe user-centered design process was instrumental in the development of the ICBT-E, by contributing to improvements of the program and to the content being adapted to the needs and preferences of end-users. The overall usability of the program was found to be good. ICBT-E targets key maintaining factors in ED by introducing healthy eating patterns and addressing over-evaluation of weight and shape. The results indicate that ICBT-E, delivered in a clinical setting, is a feasible and promising treatment for full or subthreshold BN or BED, with a high level of acceptability observed and treatment completion of 73.2 %. Participation in ICBT-E was associated with significant symptom reductions in core ED symptomology, functional impairment as well as depressive symptoms, and the results were maintained at the 3-month follow-up.ConclusionsICBT-E was developed with end-users' preferences in mind, in accordance with the identified recommendations, and the program was perceived as usable by end-users. The study demonstrated the potential of ICBT-E, which marks a step forward in the effort to make powerful, empirically supported psychological interventions targeting ED more widely available and accessible.