Thirty-nine female out-patients with bulimia nervosa were assessed for personality disorders using the PAS. All subjects then entered a therapeutic trial, comprising eight weeks of cognitive-behavioural therapy with follow-up after eight weeks and at one year. Thirty-nine per cent of the patients were diagnosed as having personality disorders. Patients with personality disorders were more depressed and had a lower BMI than those without. They also had a significantly poorer response to treatment, but the difference between groups did not reach significance when mood and BMI were controlled for. Personality disorder alone does not predict a poor response to treatment, but comorbidity with depression and low weight increases the likelihood of a poor response; these patients are unlikely to respond to brief psychotherapeutic interventions.