Internet-based cognitive behavioral therapy (ICBT) for bulimic eating disorders has demonstrated clinical utility and cost efficiency, but is associated with low patient preference, low credibility, sizeable dropout and only moderate symptom reduction. To improve outcome it is imperative to learn more about who might benefit from internet-based interventions. To do this, the current study investigated the Five Factor Model of personality as predictor of outcome in patients with full or sub-threshold bulimia nervosa (n = 109). Patients in a randomized controlled trial of ICBT were assessed prior to and at the end of treatment. Patients showed significant symptom reduction over time (Cohen's d = 1.0, p < .001). Remission as well as overall symptom reduction was positively predicted by Openness to Experience and Conscientiousness. Binge eating cessation specifically, was positively predicted by Extraversion. The study supports the use of personality assessment for patient selection and outcome optimization in internet-based treatment of bulimic eating disorders.