ObjectiveCognitive behaviour therapy (CBT) online guided self‐help programs represent efficacious and accessible treatment options for adults with binge‐eating disorder (BED), but research on predictors of treatment outcome is scarce. This study aimed to investigate the predictive value of emotion regulation difficulties relative to that of negative mood on short‐ and longer‐term treatment outcomes in an online guided self‐help programme for BED above and beyond other predictors (age, sex, baseline BED severity).MethodsParticipants were 63 adults (87% female, mean age 37.2 years) with BED. Data was analysed using a hierarchical model approach.ResultsEmotion regulation difficulties better predicted both weekly binge‐eating frequency and eating disorder (ED) pathology at posttreatment than negative mood, after controlling for the effect of age, sex and baseline BED severity. At 6‐month follow‐up, neither emotion regulation difficulties nor negative mood further added to the prediction of weekly binge‐eating frequency, whereas negative mood, but not emotion regulation difficulties, did so for ED pathology.ConclusionThese findings indicate that emotion regulation difficulties at treatment begin might be a relevant predictor of immediate treatment outcome in online guided self‐help for adults with BED but might have lower impact on longer‐term treatment outcome than negative mood.Clinical trial register numberThe clinical trial register number is not given in this version of the manuscript due to anonymisation.