This multi-level meta-analysis tested if evidence-based trauma treatment was effective in reducing trauma symptoms and externalizing behavior problems in adolescents. Based on eight independent samples and 75 effect sizes, results indicated that Trauma Focused-Cognitive Behavioral Therapy (TF-CBT) and Eye Movement Desensitization Reprocessing (EMDR) had a large and significant overall effect (d=0.909) on reducing trauma symptoms and externalizing behavior problems. Trauma treatment significantly decreased trauma symptoms (large effect) and externalizing behavior problems (medium effect). Age and type of control group moderated treatment effects. Treatment was more effective in older adolescents. Trauma treatment for adolescents with externalizing behavior problems had a larger effect compared to no treatment, but not compared to treatment as usual. It seems important to provide a broad treatment offer for adolescents with severe externalizing behavior problems, in which, besides trauma treatment, attention is paid to reducing relevant individual risk factors for behavior problems