VOL. 40, NO. 4 Comprehensive Psychiatry (Official Journal of the American Psychopathological Association) JULY/AUGUST Axis I Diagnostic Comorbidity and Borderline Personality Disorder Mark Zimmerman and Jill I. Mattia Borderline personality disorder (PD) has been the most studied PD. Research has examined the relation- ship between borderline PD and most axis I diagnostic classes such as eating disorders, mood disorders, and substance use disorders. However, there is little infor- mation regarding the relationship of borderline PD and overall comorbidity with all classes of axis I disorders assessed simultaneously. In the present study, 409 patients were evaluated with semistruc- tured diagnostic interviews for axis I and axis II disorders. Patients with a diagnosis of borderline PD versus those who did not receive the diagnosis were assigned significantly more current axis I diagnoses (3.4 v2.0). Borderline PD patients were twice as likely to receive a diagnosis of three or more current axis I disorders (69,5% v 31.1%) and nearly four times as likely to have a diagnosis of four or more disorders (47.5% v 13.7%}. In comparison to nonborderline PD patients, borderline PD patients more frequently re- ceived a diagnosis of current major depressive disor- der (MDD}, bipolar I and II disorder, panic disorder with agoraphobia, social and specific phobia, posttrau- matic stress disorder (PTSD), obsessive-compulsive disorder (OCD), eating disorder NOS, and any somato- form disorder. Similar results were observed for life- time diagnoses. Overall, borderline PD patients were more likely to have multiple axis I disorders than nonborderline PD patients, and the differences be- tween the two groups were present across mood, anxiety, substance use, eating, and somatoform disor- der categories. These findings highlight the impor- tance of performing thorough evaluations of axis I pathology in patients with borderline PD in order not to overlook syndromes that are potentially treatment- responsive. Copyright © 1999 by W.B. Saunders Company E PIDEMIOLOGICAL and clinical studies have established that comorbidity among the axis I disorders is frequent. There are several reports from the Epidemiological Catchment Area Study exam- ining lifetime comorbidity rates in individuals with a lifetime history of particular disorders. For ex- ample, Davidson et al. 1 found that 84.5% of social phobics had a history of another DSM-III disorder, the most frequent being simple phobia (60.8%), agoraphobia (45.0%), generalized anxiety disorder ([GAD] 26.9%), obsessive-compulsive disorder ([OCD] 18.6%), alcohol abuse/dependence (17.2%), and major depressive disorder ([MDD] 14.6%). Weissman et al. 2 reported that 77.1% of individuals with dysthymic disorder had at least one other lifetime disorder, the most frequent being MDD (38.9%) and substance use disorders (29.8%). Likewise, between 66% and 80% of individuals with a lifetime history of other disorders such as MDD, posttraumatic stress disorder (PTSD), and panic disorder had one or more comorbid disor- ders. 3-5 High comorbidity rates likewise have been found in the National Comorbidity Study. Kessler et al. 6 indicated that 56% of individuals with a lifetime history of any DSM-III-R disorder had at least two additional lifetime disorders. Fifty-six percent of individuals with MDD at the time of evaluation had at least one additional current disorder. 7 A lifetime history of at least one other disorder was present in 88% and 79% of men and women, respectively, with a lifetime history of PTSD, 8 and 87%, 83%, and 81% of individuals with a lifetime history of agoraphobia, simple phobia, and social phobia, respectively, had a lifetime history of at least one other disorder. 9 From the Department of Psychiatry and Human Behavior, Brown University School of Medicine, Rhode Island Hospital, Providence, R1. Supported in part by National Institute of Mental Health Grant No. MH-48732 (M.Z ). Address reprint requests to Mark Zimmerman, M.D., Bayside Medical Center, 235 Plain St, Providence, R102905. Copyright © 1999 by W.B. Saunders Company 0010-440X/99/4004-0011 $10. 00/0 ComprehensivePsychiatry, Vol. 40, No. 4 (July/August), 1999: pp 245-252 245