There are contradictory results concerning the frequency of borderline personality disorder (BPD) in bulimic patients and its impact on eating pathology and treatment outcome. We evaluated 240 patients with bulimia nervosa using EDI-2, SIAB and SCL-90-R. Only a minority of patients had a BPD (13.8%). There were no differences in binging or purging behaviour between patients with and without BPD, but borderline patients had significantly more feelings of ineffectiveness and more disturbances in interoceptive awareness. Bulimic patients with BPD showed significantly more general psychopathology. Although, BPD patients started with higher levels of pathology, there were similar reductions of symptoms over the course of treatment in both groups. Psychotherapy in bulimic patients with a BPD has to focus not only on eating pathology but also on aspects that are caused by the severe personality disturbance. Copyright © 2007 John Wiley & Sons, Ltd and Eating Disorders Association.