The purpose of this study was to assess the prevalence of each of the nine DSM criteria for borderline personality disorder and the prevalence of the disorder itself in the first-degree relatives of borderline probands and Axis II comparison subjects. Four hundred and forty-five inpatients were interviewed about familial borderline psychopathology using the Revised Family History Questionnaire--a semistructured interview of demonstrated reliability. Of these 445 subjects, 341 met both DIB-R and DSM-III-R criteria for BPD and 104 met DSM-III-R criteria for another type of personality disorder (and neither criteria set for BPD). The psychopathology of 1,580 first-degree relatives of borderline probands and 472 relatives of Axis II comparison subjects was assessed. Both DSM-III-R and DSM-IV BPD were found to be more common among the relatives of borderline than Axis II comparison probands. However, five of the criteria for BPD (inappropriate anger, affective instability, paranoia/dissociation, general impulsivity, and intense, unstable relationships) and all four sectors of borderline psychopathology (affect, cognition, impulsivity, and interpersonal relationships) were found to be both more common and discriminating than the BPD diagnosis itself. Taken together, the results of this study suggest that the subsyndromal phenomenology of BPD may be more common than the borderline diagnosis itself.