Access to Mental Health and Addiction (MHA) services have been identified as a priority within First Nations communities. Consequently, there is a need for a focused report assessing MHA service use and system performance. A request was submitted to ICES by the Chiefs of Ontario to replicate an Ontario Mental Health Scorecard1 using First Nations identifiers across the lifespan. The Indian Register (IR) has been linked with ICES health administrative data and is used to identify First Nations people in Ontario with a history of MHA-related service use and outcomes. ICES received approval from the Chiefs of Ontario to use the IR for this project on March 12, 2018. It examines rates of mental health service use and median length of hospital stay for First Nations people, compared to non- First Nations people and to Ontario overall. This is the first project to assess MHA-related performance indicators and factors relating to those indicators among the First Nations population in Ontario.