OBJECTIVES: The CREDO trial demonstrated the clinical efficacy of 12-month therapy with clopidogrel, with a 27% RRR (p=0.02) combined risk of death, MI, or urgent target revascularization in patients undergoing percutaneous coronary intervention (PCI) and being treated with ASA. The purpose of this study was to evaluate the long-term cost-effectiveness of 12-month versus 28-day therapy with clopidogrel in Sweden. METHODS: A Markov model was developed, enabling modelling over the longer term. A hypothetical cohort of patients in a post-PCI state were assumed to have certain risks of suffering one of the endpoints of the CREDO trial: stroke, MI or death. First-year risks were taken from the observed rates of the CREDO trial while risks for following years were estimated based on epidemiological data, provided by the Centre for Epidemiology at the Swedish National Board of Health and Welfare. Cost data was collected from published sources. The perspective was that of society. Effectiveness was measured as the number of life-years gained from long-term treatment with clopidogrel. Cost-effectiveness acceptability curves were created using bootstrapping to estimate parameter uncertainty and Monte Carlo simulation to estimate the effect of this uncertainty in the model. RESULTS: The model predicted a mean survival of 12.35 years in the 12-month arm compared to 12.28 in the 28-day arm, an incremental gain of 0.065 life-years. The increase in survival came at a predicted incremental cost of 171€, resulting in an incremental cost-effectiveness ratio (ICER) of 2637€. If only direct costs were considered, the ICER was 7588€. If costs due to increased survival were included, the ICER was 14,681€. Results were insensitive to variations in costs and discount rates. CONCLUSIONS: The predicted cost-effectiveness ratio of long-term treatment with clopidogrel in patients undergoing PCI is well below the threshold values currently considered cost-effective.