The aim of this study is to explore the prevalence of Dual Diagnoses (substance use disorder/addiction and mental health conditions) and ACE (trauma/adverse childhood experiences) in a residential addiction treatment population. The impetus for this study stems from a changing perspective on how we understand the relationship between mental health and addiction. Increasingly, clients present with complex needs within drug and alcohol addiction treatment services. The outcomes of this study will identify current profiles of 50 adults seeking residential treatment services and this may be relevant for both the service design and delivery. By increasing awareness of theory and practice of the complex phenomena of Dual Diagnosis and exploring the relationship between ACE and addiction/ mental health, services can cater for the complexity of client needs, thus supporting improved health outcomes.