Objective: Previous research on the prevalence of personality disorders in patients with eating disorders varies greatly in findings, but a general understanding seem to exist that personality disorders are rather common among eating-disordered patients. The present investigation is aimed at establishing the prevalence of DSM III-R or DSM IV personality disorders in a large population seeking treatment for eating disorders. Method: Five hundred and forty-five patients with DSM IV-eating disorders have been evaluated using the structured clinical interview for DSM III-R or IV-Axis II and the eating disorder examination. Results: The 29.5% of the population have one or more personality disorders according to DSM III-R or DSM IV criteria. Personality disorders, and specifically borderline personality disorder, are significantly more common in patients with bulimia nervosa. Discussion: The proportion of eating-disordered patients with co-morbid personality disorder may not be as large as often found in studies. This challenges the understanding of a strong overall connection between the two groups of disorder; however, the connection seems to exist in subsets of eating disorder samples. Copyright (C) 2007 John Wiley & Sons, Ltd and Eating Disorders Association.