This study demonstrates inherent features in the DSM-III diagnostic criteria for personality disorders (i.e., overlapping diagnoses and heterogeneous symptomatology) that limit efforts to identify a sensitive and specific MMPI profile for the borderline personality disorder. A sample of 71 inpatients was administered an MMPI and a semistructured interview that systematically evaluated each of 81 symptoms for the 11 DSM-III personality disorders. Interrater reliability was substantially higher than has been obtained with unstructured interviews. The effect on the borderline MMPI profile of variation in the number of borderline symptoms and overlap with the schizotypal, histrionic, and antisocial diagnoses was demonstrated. We discuss implications with respect to a prototypal model of classification.