In this article, we review the clinical research on the implications of comorbid personality disorders (PDs), pathological personality traits, and the expression and response to treatment of those with eating disorders (EDs) (i.e., anorexia and bulimia nervosa, and binge eating disorder). Obsessive-compulsive PDs and related traits, such as perfectionism and rigidity, appear to be clear-cut risk and maintenance factors for anorexia nervosa. In bulimia nervosa, trait impulsivity seems to be related to early termination from therapy and, according to at least some indices, poorer responses to treatment. Dramatic-Erratic PD features, generally more characteristic of binge-purge ED variants, clearly predict a protracted course for general psychiatric symptoms, but may have less prognostic value for eating symptoms. Recent guidelines from two influential bodies--the American Psychiatric Association (APA, 2000) and the United Kingdom's National Institute for Clinical Excellence (NICE, 2004)--both include the concept that "trait-oriented" interventions, targeting personality-linked components like perfectionism, affective instability, impulsivity, and interpersonal disturbances, may optimize treatment effects. In general, the literature supports the recommendation that clinicians should apply well-validated, symptom-focused therapies for the EDs; in addition, clinicians may wish to incorporate trait-focused interventions in patients in whom personality pathology contributes to suboptimal response.