OBJECTIVES: Low-dose Aspirin is standard care in patients with a history of cardiovascular disease (CVD). In primary prevention the use of low-dose Aspirin is not yet fully established although meta-analyses and US and European guidelines support its use in persons at increased CVD risk. This study assessed the health economic consequences of the use of low-dose Aspirin in the primary prevention of CVD in the UK. METHODS: Based on results (benefits and harms) reported in the meta-analyses of Hayden (2002) and Eidelman (2003), a Markov model was developed to predict the cost-effectiveness of low-dose Aspirin in the primary prevention of CVD. The model consists of 5 health states: no history of CVD, history of stroke, history of myocardial infarction, history of CVD and death. A 10-year time horizon and 1-year cycles were used. Secondary prevention data were derived from the Aspirin group of the CAPRIE-study (1996). Direct costs from the NHS (2003) perspective were used. Effects were expressed in Life-Years Gained (LYG) and Quality-Adjusted-Life-Years Gained (QALY). Utility data (TTO) were obtained from published data. Discounting was applied (3.5% on effects and costs). RESULTS: For patients with a 10-year risk of coronary heart disease (CHD) of 15% the model results in a 10-year cost of GBP899±44 (1,360±64€) without and GBP767±53 (1,163±81€) with Aspirin. Low-dose Aspirin treatment saves on average GBP115 per patient. LYG were respectively 8.17±0.01 and 8.19±0.02, QALYG 8.04±0.02 and 8.08±0.03. Monte Carlo analysis showed Aspirin-dominance in 96.7% of cases. Savings start in the first year. Treating all UK individuals with a risk ≥15% would result in at least GBP1.5 billion of savings over 10 years. CONCLUSIONS: Administering low-dose Aspirin to patients with a 10-year risk of CHD of 15% and more is significantly cost-saving from the NHS perspective. Sensitivity analyses (CHD risk and bleedings) proved robustness of the results.