Background: This study examines newcomers with intellectual and developmental disabilities compared to other adults with intellectual and developmental disabilities in Ontario, Canada. Methods: This population-based retrospective cohort study used linked health and social services administrative data to identify adults with intellectual and developmental disabilities as newcomers, or non-newcomers, and compared their health status and health service outcomes. Results: Among those with intellectual and developmental disabilities, compared to non-newcomers, newcomers generally had lower or similar rates of health issues, except for higher rates of psychosis. Newcomers also had slightly greater use of community-based health services, but less hospital use. Conclusion: Trends among those with the intellectual and developmental disabilities were consistent with general population trends; newcomers had lower rates of many health issues and lower hospital use. It also underscores the value of understanding drivers of heterogeneity within newcomers, such as the circumstances of admission and settlement in their new country.