OBJECTIVE: To determine the patterns of aspirin use for the primary prevention of coronary heart disease (CHD). Aspirin for primary prevention has a more favorable risk/benefit profile among adults with high CHD risk than among low-risk adults. METHOD: We studied 5725 adults aged 35-75 without cardiovascular disease in a population-based study in Switzerland in 2003-2006. We examined regular aspirin use for cardiovascular prevention according to 10-year CHD risk and other cardiovascular risk factors. RESULTS: One hundred seventy-four participants used aspirin. Aspirin use increased with 10-year CHD risk, from 2.6% in persons with risk <6% (low risk) to 9% in those with risk 6-20% (intermediate risk, p=0.001), but no adults with risk >/=20% used aspirin. Participants with cardiovascular risk factors were more likely to use aspirin. However, 1.9% adults with risk <6% and no diabetes used aspirin. Using a population perspective, a more appropriate aspirin use would reduce up to 2,348/24,310 CHD deaths expected over 10 years in Switzerland, and avoid about 700 gastrointestinal bleedings and hemorrhagic strokes among those not eligible. CONCLUSION: Individuals at intermediate CHD risk and diabetics are more likely to take aspirin, but there are significant opportunities for improvement. The underuse of aspirin for those at risk coexists with an overuse among those at low risk.