Inhibitors of the renin-angiotensin system remain a cornerstone of cardiovascular pharmacotherapy. Although angiotensin converting enzyme inhibitors (ACEIs) have been demonstrated to afford cardiovascular risk reduction in patients with atherosclerosis and preserved left ventricular function, at the present time it is unclear if angiotensin receptor blockers (ARBs) exert similar benefits. We performed a population-based comparative study to compare the rates of hospital admission for acute coronary syndromes between users of ARBs relative to the use of ACEIs. A retrospective cohort study using population-based administrative databases in Ontario, Canada covering over 1.4 million residents age 65 years and older with access to universal healthcare coverage was conducted. We compared the hospital admission for acute coronary syndromes (ACS) among patients initiated on ARBs as compared to propensity-score matched patients started on ACEIs from 1999 through 2002, using a 3:1 (ACEI:ARB) matching strategy. Each individual was observed for up to 2 years. The primary outcome of interest was an ACS event, defined as the composite of hospital admission for myocardial infarction and/or unstable angina. During over 71,000 person-years of follow-up, we observed 1,295 hospitalizations for ACS. Relative to ACEI users (n = 49,037), rate of hospitalizations for ACS was similar in patients initiated on ARBs (n = 16,456) (adjusted relative risk [aRR] 0.89, 95% confidence interval [CI] 0.76-1.04. Pre-specified secondary analysis, performed in patients with atherosclerosis, diabetes, and heart failure, also revealed no difference in rates of myocardial infarction and acute coronary syndromes in users of ARBs compared to ACEIs (adjusted relative risk, diabetes: 0.79, 95% CI 0.58-1.07; heart failure: 0.84, 95% CI 0.59-1.20; atherosclerosis: 0.85, 95% CI 0.70-1.04). These data represent the first and largest population based comparative evaluation of ACEI and ARBs on hospitalizations for ACS among new users of each therapy. Our findings suggest that ARBs offer similar reduction in acute coronary syndrome outcomes in elderly patients with atherosclerosis, diabetes or heart failure. These data have important clinical implications, especially since patients over the age of 65 represent the largest users of risk reduction therapy.