Despite substantial evidence that antiplatelet therapy saves lives and reduces adverse events in patients with coronary artery disease (CAD), use of the most widely available and lowest cost antiplatelet agent, aspirin, continues to be disappointingly low. In a large database of patients with known CAD, we (1) explored trends in the use of aspirin over time, (2) characterized patients most likely to take aspirin regularly, and (3) estimated the effectiveness of aspirin use by examining long-term outcomes. Using patients entered in the Duke Databank for Cardiovascular Diseases, we explored the use of aspirin from 1969 to 1999. More than 25,000 patients were sent a questionnaire that included several questions about medication use, including 1 question specifically about aspirin. Patients who failed to respond to the questionnaire received a follow-up telephone call. Aspirin use increased substantially over the most recent 4 years in the study, from 59% in 1995 to 81% in 1999. Predictors of aspirin use included younger age, male sex, being a nonsmoker, and having had a myocardial infarction or revascularization procedure. Patients who never took aspirin had a risk ratio for death of 1.85 compared with patients who regularly took aspirin. Despite the well-known beneficial effects of aspirin, too many patients without contraindications to aspirin fail to take it regularly. The health care system currently lacks effective methods to ensure that patients who have CAD have adequate follow-up concerning aspirin use.