Based on the results of the Physician's Health Study, the US Preventive Services Task Force currently recommends low doses of aspirin on alternate days for men over age 50 years to prevent first myocardial infarction. Although there are no clinical trials involving women, three female cohort studies of aspirin and prevention of myocardial infarction have been published with conflicting results. We conducted a critical review of the three female cohort studies. Although a general recommendation for asymptomatic women to take aspirin to prevent myocardial infarction is not currently indicated, the best available data suggest a beneficial effect, particularly in women at high risk of coronary artery disease. The clinician should therefore consider aspirin use in each patient individually.