Eligible participants were community-dwelling adults from Australia and the United States who were 70 years of age or older (or ≥65 years of age among blacks and Hispanics in the United States). Eligibility criteria are provided in Table S1 in the Supplementary Appendix, available at NEJM.org. Participants were required to be free from overt coronary heart disease, overt cerebrovascular disease, atrial fibrillation, a clinical diagnosis of dementia, clinically significant physical disability, a high risk of bleeding, anemia, and a known contraindication to or inability to take aspirin. Key exclusion criteria were the current regular use of an anticoagulant or antiplatelet medication other than aspirin, a systolic blood pressure of 180 mm Hg or more or a diastolic blood pressure of 105 mm Hg or more, a medical indication for or contraindication to regular aspirin therapy, or the presence of a condition that, in the opinion of the primary care physician, was likely to result in death within 5 years. Participants were allowed to take other nonsteroidal antiinflammatory drugs (NSAIDs), with the recommendation to take the lowest dose for the shortest duration necessary.