Individuals with both psychiatric and substance use disorders, defined as concurrent disorders, are more complex to diagnose and treat due to several interacting health and social challenges. In the absence of appropriate treatment people with concurrent disorders are at high risk for increased morbidity and mortality. A growing body of evidence recommends abandoning the traditional single-disease health model in favour of a multimorbidity approach to care. Despite available evidence, important gaps persist in our understanding of how individual and health system context influence service utilization and outcomes for people with complex multimorbid disorders (e.g. concurrent disorders). The proposed research will establish a prospective cohort of individuals with a concurrent disorder. Individuals will complete a series of brief questionnaires and provide consent to use their personal identifiers for linkage to a number of health databases. This research offers a unique opportunity examine health outcomes associated with multi-morbidities and understand patterns of health care utilization overtime. This research will advance knowledge to inform best practices and service reforms for the optimal delivery of care in BC.