OBJECTIVE: To examine trajectories of treatment response in suicidal youth who participated in a randomized controlled trial comparing dialectical behavior therapy (DBT) and individual and group supportive therapy. METHOD: Using latent class analysis across both treatment conditions, secondary analyses were conducted of data from a multisite randomized controlled trial comprising 173 youths ages 12-18 with repetitive self-harm (SH) (including ≥1 lifetime suicide attempts) and elevated suicidal ideation (SI). The sample was 95% female, 56.4% White, and 27.49% Latina. Participants received 6 months of DBT or individual and group supportive therapy and 6 months of follow-up. Primary outcomes were SH and SI. RESULTS: Of the sample, 63% and 74% were members of latent classes that showed improvement in SI and SH, respectively; 13% were total nonresponders, with no improvement in SI or SH. SH nonresponse emerged at the midpoint of treatment (3 months), with nonresponders showing a sharp increase in SH over the remainder of treatment and follow-up. Youth receiving DBT were significantly more likely to be an SH responder vs nonresponder than youths in individual and group supportive therapy (ꭓ = 6.53, p = .01). An optimal threshold cut point using multivariate predictors of total nonresponse (White, externalizing symptoms, total SH, and SI) predicted total nonresponders to DBT with 100% accuracy. CONCLUSION: This is the first study to identify trajectories of both SI and SH response to treatment in a sample of adolescents at risk of suicide. Results may inform personalized treatment approaches. CLINICAL TRIAL REGISTRATION INFORMATION: Collaborative Adolescent Research on Emotions and Suicide (CARES); https://www. CLINICALTRIALS: gov/; NCT01528020.