<p>Adolescents with suicidal and self-harming behavior run significant risk for suicide. Outcomes in adult life after specialized treatment for this population are unknown. We examined adult life outcomes in adolescents with recurrent suicidal and self-harming behavior and borderline features having participated in a randomized trial of dialectical behavior therapy (DBT-A) or enhanced usual care (EUC). Of the original 77 study participants, 61 (79%) were followed-up at a mean age of 28&#xa0;years, an average of 12.4&#xa0;years post-baseline. Primary outcomes were frequency of self-harm episodes and levels of suicidal ideation and depressive symptoms over the follow-up intervals. Secondary outcomes were borderline symptoms, psychiatric morbidity, occupational and psychosocial functioning. Self-harm frequency was consistently lower throughout the 12.4&#xa0;year follow-up period in participants who had received DBT-A, although differences were not statistically significant at the final follow-up. Whereas suicide attempts were infrequent in both groups, self-harm episodes were more than twice as common in the EUC group compared to the DBT-A group with a mean difference of 90 episodes per person from baseline to 12.4&#xa0;years follow-up. DBT-A was associated with significantly stronger reductions in suicidal ideation, depressive and borderline symptoms at end of treatment but differences tapered off until not statistically significant at the final follow-up. There were no significant trend differences in current psychiatric morbidity, self-reported depressive symptoms and global functioning. This first study of adult life outcomes of specialized psychosocial interventions for adolescents with recurrent suicidal and self-harming behavior and borderline features suggests that adolescents may have a realistic hope of sustained recovery as adults.</p><p>Trial Registration: <a href="http://ClinicalTrials.gov/;NCT04298190">http://ClinicalTrials.gov/;NCT04298190</a></p>