Two self-report questionnaires (MCMI and BSI) designed to measure personality disorder (PD) according to DSM-III (R) criteria were administered to patients with a diagnosis of anorexia nervosa (AN) (n = 19), bulimia nervosa (BN) (n = 16), or both diagnoses (AN + BN) (n = 9), both before and after treatment for the eating disorder. The main finding was that self-reported Personality Disorder (PD) diagnoses are not stable enduring characteristics among this group of eating disorder patients. A high rate of PD diagnoses occurred in all patient groups at admission (93%) and at discharge (79%). Both MCMI and BSI scales were subject to significant change following treatment. A high prevalence of borderline personality disorder was found in patients with BN. Changes in depression and self-esteem scores correlated most strongly with changes in schizoid, schizotypal, histrionic and narcissistic scales. Assessment of PD using self-report measures should be interpreted with caution in acutely symptomatic patients with eating disorders.