Under Australia's National Illicit Drug Strategy, a National Comorbidity Initiative was established to improve service coordination and treatment outcomes for people with coexisting mental health and substance use disorders. A priority area under this Initiative is to improve data systems and collections methods within the mental health and alcohol and other drug sectors to manage comorbidity more effectively.This project, commissioned by the Australian Government Department of Health and Ageing, identifies, reviews and reports on the current state of data collections relating to people with coexisting substance use and mental health disorders ('comorbidity') in Australia.