OBJECTIVE: The purposes of this study were to evaluate the use of an online guided self-treatment programme for bulimia nervosa (BN) and to determine predictors of outcome. Data were collected in four European countries where the programme was simultaneously used. METHOD: One hundred and twenty-seven BN or subthreshold BN female patients (mean age of 24.7 years) participated in a 4-month intervention using a CBT based online-guided self-help programme. Contact during the treatment period included weekly e-mails with a coach. ASSESSMENT: Measures included the Eating Disorders Inventory-2 (EDI-2) and the Symptom Check List-Revised (SCL-90R). RESULTS: Severity of eating disorders symptoms and general psychopathology improved significantly. Twenty-three per cent of patients were symptom free at the end of treatment. The dropout rate was 25.2%. A better score of general psychological health was a predictor of a better outcome. CONCLUSIONS: This study encourages further developments and research on innovative therapy approaches, particularly for those disorders such as BN, with difficult therapy and unclear prognosis. Copyright © 2010 John Wiley & Sons, Ltd and Eating Disorders Association.