To determine whether sex differences exist in the use of coronary angiography, coronary artery bypass surgery (CABS) or percutaneous transluminal coronary angioplasty (PTCA) among persons recently diagnosed with an acute myocardial infarction (AMI) in Canada. A growing body of literature suggests that coronary artery disease in males is treated differently from females. Specifically, recent studies have indicated that sex may influence decisions about the use of invasive diagnostic and therapeutic coronary procedures in patients with suspected or proven coronary artery disease. The study design is a population-based inception cohort study. The data source is hospital discharges from all acute care hospitals in Ontario. The study population consisted of 6949 men and women discharged with a principal diagnosis of AMI between April 1 and September 30, 1990, and followed through record linkage until March 31, 1991 to determine whether any invasive coronary procedures were performed after their AMI. Odds ratio estimates (OR) and 95% confidence intervals (95% CI) for use of coronary angiography, CABS and PTCA in men were compared with those in women. The adjusted OR for coronary angiography was 1.4 (95% CI 1.2 to 1.6), indicating that males were more likely to undergo angiography than females. A similar finding was seen for CABS (OR = 1.6, 95% CI 1.2 to 2.1), but for PTCA, the sex difference was less pronounced (OR = 1.3, 95% CI 1.0 to 1.7). Cox proportional hazards regression also was used to test the hypothesis and showed similar results. Women suffering AMI undergo coronary angiography and CABS at a significantly lower rate than men in Ontario, with similar trends evident in use of PTCA.