This clinical research report identified 4 subcategories of the hospitalized borderline personality disorder: developmental, affective disorder, attentional deficit/learning disabled, and organic. Developmental and affective disorder subcategories are predominantly composed of females, while males are overly represented in the attentional deficit/learning disabilities subcategory. Comparison of the borderline patients with schizophrenic and affective disorder control groups supports the hypothesis that the borderline personality disorder is a diagnostic entity distinct from schizophrenia, but perhaps not from affective disorders.