The Personality Disorders Examination (PDE) was administered to 71 bulimia nervosa patients at baseline assessment in a study comparing the effectiveness of cognitive-behavioral treatment with desipramine or the combination of both treatments. Personality disorder subscales were combined into single DSM-III-R cluster scores. A high cluster B score (consisting of antisocial, borderline, histrionic, and narcissistic features) significantly predicted poor outcome at 16 weeks and was a better predictor of outcome than borderline personality characteristics alone or any other DSM-III-R cluster score or combination of cluster scores. In contrast pretreatment depression level, self-esteem, degree of dietary restraint, frequency of purging, and history of anorexia nervosa were not significantly related to outcome. At 1-year follow-up there was still a trend toward high cluster B scores predicting poor treatment outcome. Cluster B score was not significantly correlated with percentage of sessions attended nor did subjects with higher cluster B scores have a better outcome with either specific treatment. These results suggest that further investigation of alternative treatments is warranted with high cluster B individuals to determine if treatment effectiveness can be improved.