Exposure to childhood adversity is a prevalent and pressing issue due to its established links with poor physical and mental health outcomes across the lifespan. High rates of adversity have been found within young people attending mental health services, and the provision of trauma-informed care and trauma-specific therapies are therefore essential within these services. Trauma-focused cognitive behaviour therapy (TF-CBT) is an evidence-based intervention with established efficacy amongst traumatised children and youth. The primary objective of this study was to evaluate the effectiveness of trauma-specific therapy (TF-CBT) when implemented in a Child and Adolescent Mental Health Service (CAMHS). Given that most youth receive care in community settings, it is important to determine whether treatments tested under controlled conditions can apply in the real world of clinical practice. Specifically, this study aimed to quantify the number and type of adversities reported by clients receiving the intervention; investigate whether the intervention is associated with improvements in participants’ posttraumatic stress disorder (PTSD) symptoms, general mental health symptoms and functioning; and report contact with CAMHS at 3 months and 2 years post-treatment. Results showed that CAMHS clients were more likely to have experienced multiple traumatic events than single events, with 100% of clients experiencing suicidal thoughts. Treatment was associated with significant improvements in PTSD symptom severity and improvements in general mental health symptoms. Many clients received ongoing mental health support at the 3-month and 2-year follow-ups, reflecting the complex nature of their issues and the need for support to maintain gains achieved during treatment.