Sixty-seven patients with bulimia nervosa and 29 patients with anorexia nervosa completed the Impulsiveness Questionnaire and questionnaires detailing severity of eating disorder. Bulimic patients had higher impulsivity scores than anorexic patients. Bulimics with high impulsivity scores did not have more severe eating disorders than low scorers. When 39 bulimics and 25 anorexics were interviewed about other impulsive behaviour, 51% of bulimics and 28% of anorexics reported at least one other impulsive behaviour. Patients with so-called 'multi-impulsive' bulimia reported more severe eating disturbance, but this was not reflected on more reliable measures of symptoms. Thirty-nine bulimics entered an eight-week treatment trial and their progress was assessed at eight weeks, 16 weeks and one year. 'Non-impulsive' bulimics had a more rapid response than 'impulsives' during treatment, but there was no difference at follow-up. There was no evidence of an association between high impulsivity trait scores and poor treatment response. It is concluded that impulsivity may shape the expression of eating disorders, but that 'multi-impulsives' do not constitute a categorically distinct subgroup of bulimics.