To the Editor: The important study by Mary C. Zanarini, Ed.D., et al. (1) demonstrated the central role of substance abuse in the course of borderline personality disorder. Although the authors stated that "this finding runs counter to clinical lore" (p. 2112), they failed to mention that a study described in one of their references (2, p. 211) found that substance abuse accounted for more of the variance in outcome for female patients with borderline personality disorder than any of the seven other factors that were studied. Taken together, these data underline the sound recommendation of Dr. Zanarini et al. that substance abuse disorders in patients with borderline personality disorder need to be a crucial focus of treatment efforts.