Suicide is the third leading cause of death among adolescents in the US yet there is a paucity of research on effective treatments for this population. The primary aim of the research described in this application is to evaluate the efficacy of dialectical behavior therapy (DBT) for suicidal adolescents. DBT has an empirical track record with suicidal adults of reducing the incidence, frequency and medical risk of suicide attempts and non-suicidal self-injuries among individuals meeting criteria for borderline personality disorder (BPD). While DBT is widely used in the community with suicidal adolescents, particularly those with difficulties characteristic of BPD such as poor emotion regulation and impulse control, no randomized trial of DBT with suicidal adolescents has ever been conducted. And, while non-randomized trials indicate that the intervention is both safe and effective, without a randomized trial the investigators simply do not know whether DBT for suicidal adolescents is efficacious or not. Given the severity of the problem and the lack of alternative treatments for high risk adolescents, addressing this question is of great importance. The second aim of the research is to analyze mediators of reduced suicidal and self-injurious behaviors in adolescents. 170 adolescents at two sites (Seattle and Los Angeles) will be randomized to DBT or Individual and Supportive Group Therapy (IGST). Both treatments include 6 months of individual and group treatment and adolescents and a parent complete 5 assessments over a 1-year period.