This study examines the course of illness and stability of borderline personality disorder (BPD) in a group of inpatients seen at a two-year follow-up. The diagnosis of borderline personality disorder, as established by the use of the Diagnostic Interview for Borderlines, did not change in 39 of the 65 subjects (60%) studied. Subjects who continued to show evidence of borderline psychopathology experienced more acute episodes of illness during the follow-up period and tended to be more involved in substance abuse. Impulsiveness and young age when first psychiatric care was received significantly predicted the presence of BPD features at follow-up.