ABSTRACT The goal of this study was to evaluate the effectiveness of dialectical behavior therapy for adolescents (DBT-A) with borderline personality disorder (BPD) features under routine health-care conditions, particularly an urban hospital that primarily treats low income and ethnic minority individuals. Ninety-one adolescents (age 11–18) participated in at least one cycle of an outpatient DBT-A program, with the option to continue in additional cycles. The majority, 39% (N = 35), identified as Hispanic/Latinx, 29% (N = 27) as non-Hispanic White, and 20% (N = 18) as Black; 84% (N = 76) identified as female. Prior to beginning treatment, adolescents completed baseline assessments on BPD symptoms (BPD subscale of the Structured Clinical Interview for DSM-IV; Life Problems Inventory), lifetime history of suicidal and non-suicidal self-injurious behaviors (Lifetime-Suicide Attempt Self-Injury Interview), depression (Beck Depression Inventory), and higher level of care utilization. After each treatment cycle, participants completed these measures again; they and their caregivers also completed a DBT acceptability questionnaire (DBT-A Satisfaction Survey). Results yielded statistical and clinical significance, and reliable change (reduction) in suicidal behavior, non-suicidal self-injurious behavior, BPD symptoms (impulsivity, identity disturbance, interpersonal problems, and emotion dysregulation), depression, and service utilization (effect sizes ranging from medium to large) with high client satisfaction. These findings expand upon previous DBT-A effectiveness research by engaging a larger and more diverse sample with broader inclusion criteria that is consistent with outpatient community settings, reporting on the clinical significance of DBT-A, and assessing outcomes beyond one cycle of treatment.