A careful study of 106 patients, diagnosed as borderline using the criteria of the Diagnostic and Statistical Manual of Mental Disorders, 3rd Edition, is in progress at a private psychiatric facility. Three distinct subcategories of the borderline personality disorder have been identified: history of no organicity, history of trauma, encephalitis, or epilepsy, and history of attentional deficit disorder/learning disabilities. A discriminant function analysis approach clearly distinguishes the three borderline subcategories from one another and from a schizophrenic control group. Borderline patients also show significant sex differences. The borderline personality disorder is viewed as either on a continuum with affective disorders and atypical psychoses, or with organic brain dysfunction including the episodic dyscontrol syndrome and/or adult minimal brain dysfunction. Future research should be directed toward further classifying homogeneous subgroups of borderline patients in order to provide more specific and effective treatment.