Objective: Cognitive Behavior Therapy (CBT) is an effective treatment for anxiety and depression disorders. Nonetheless, nearly 50% of all patients do not respond. Besides other factors, this seems to be linked to the experience of traumatic life events. This study aims to assess the effects of trauma history on the choice of therapy interventions and treatment outcomes. Methods: We analyzed data from 340 CBT outpatients diagnosed with a depression or anxiety disorder and possibly a trauma history treated under naturalistic conditions. Based on their written therapy files, we collected information on trauma history, psychiatric diagnoses, duration of therapy, applied interventions, and severity of depression and anxiety symptoms at the start and end of therapy. The influence of trauma, diagnoses, and intervention use on the development of depression and anxiety symptoms were analyzed. Results: Patients with a trauma history reported higher overall depression and anxiety symptoms than those without trauma. No differences in the duration of therapy, applied interventions, or decrease in symptom severity were found between patients with and without a trauma history. Trauma-specific interventions failed to boost treatment success; however, they were also seldom applied. Conclusion: Although no differences between traumatized and non-traumatized patients were found for naturalistic CBT, traumatized patients maintained higher levels of symptom severity irrespective of diagnoses. These results indicate a need for more trauma-specific and personalized interventions. Therapists may need evidence-based guidelines to personalize CBT for patients with a trauma history and high symptom severity.