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Background: New immigrants to North America exhibit lower rates of obesity and hypertension than their native-born counterparts. Whether this is reflected by a lower relative risk of acute myocardial infarction (AMI) is not known. Objective: To determine the risk of AMI among new immigrants compared to long-term residents, and, among those who develop AMI, their short- and long-term mortality rate. Design: Population-based, matched, retrospective cohort study. Setting: Entire province of Ontario, the most populated province in Canada, from 1 April 1995 to 31 March 2007. Participants: A total of 965 829 new immigrants were matched to 3 272 393 long-term residents by year of birth, sex and geographic location. Measurements: The main study outcome was hospitalization with a most responsible diagnosis of AMI. Secondary study outcomes among those who sustained an AMI were in-hospital, 30-day and 1-year mortality. Results: The mean age of the participants at study entry was ∼34 years. The incidence rate of AMI was 4.14 per 10 000 person-years among new immigrants and 6.61 per 10 000 person-years among long-term residents. After adjusting for age, income quintile, urban vs. rural residence, history of hypertension, diabetes mellitus and smoking and number of health insurance claims, the hazard ratio for AMI was 0.66 [95% confidence interval (CI): 0.63-0.69]. Conclusion: New immigrants appear to be at lower risk of AMI than long-term residents. This finding does not appear to be explained by the availability of health-care services or income level. [ABSTRACT FROM AUTHOR]