• To test the validity of the DSM-III diagnosis of borderline personality disorder (BPD), we examined the phenomenology, family history, treatment response, and four-to-seven-year long-term outcome of a cohort of 33 patients meeting DSM-III criteria for BPD. We found that (1) BPD could be distinguished readily from DSM-III schizophrenia; (2) BPD did not appear to represent "borderline affective disorder," although many patients displayed BPD and major affective disorder concomitantly; and (3) BPD could not be distinguished on any of the Indices from histrionic and antisocial personality disorders.