This study evaluated whether dialectical behavior therapy (DBT) was more efficacious than treatment by nonbehavioral psychotherapy experts in reducing co-occurring Axis I disorders among suicidal individuals with borderline personality disorder (BPD). Women with BPD and recent and repeated suicidal and/or self-injurious behavior (n = 101) were randomly assigned to 1 year of DBT or community treatment by experts (CTBE), plus 1 year of follow-up assessment. For substance dependence disorders (SDD), DBT patients were more likely to achieve full remission, spent more time in partial remission, spent less time meeting full criteria, and reported more drug- and alcohol-abstinent days than did CTBE patients. These findings suggest that improvements in co-occurring SDD among suicidal BPD patients are specific to DBT and cannot be attributed to general factors associated with nonbehavioral expert psychotherapy. Further, group differences in SDD remission were not explained by either psychotropic medication usage or changes in BPD criterion behaviors. DBT and CTBE did not significantly differ in the reduction of anxiety disorders, eating disorders, or major depressive disorder. (Contains 2 figures, 7 tables, and 2 footnotes.)