The long-term use of aspirin (ASA) reduces the risk of subsequent acute coronary syndromes in patients with coronary artery disease (CAD). It is less clear whether ASA therapy benefits patients who develop an acute coronary syndrome despite its use. Baseline characteristics, type of acute coronary syndrome, and in-hospital events were compared on the basis of previous use of ASA in 11,388 patients with and without a history of CAD presenting to 94 multinational hospitals. A total of 73.0% of patients with a history of CAD (n = 4,974) were previously on long-term ASA therapy compared with 19.4% of patients without a history of CAD (n = 6,414). After multivariate regression analysis controlling for various potentially confounding factors, patients with a history of CAD who were previously taking ASA were significantly less likely to present with ST-segment elevation myocardial infarction (MI) (adjusted odds ratio [OR] 0.52, 95% confidence intervals [CI] 0.44 to 0.61) or die during hospitalization (OR 0.69, 95% CI 0.50 to 0.95) in comparison to patients who were not taking ASA. Patients without a history of CAD and who were previously taking ASA also had a lower risk of developing ST-segment elevation MI (OR 0.35, 95% CI 0.30 to 0.40) and a trend toward a decreased hospital death rate (OR 0.77, 95% CI 0.55 to 1.07). These results demonstrate that patients with a history of CAD who present with an acute coronary syndrome despite prior ASA use have less severe clinical presentation, fewer hospital complications, and lower in-hospital death rates than patients not previously taking ASA.