OBJECTIVE: To estimate the cost effectiveness of treatment with n-3 polyunsaturated fatty acids (n-3 PUFA) for secondary prevention after myocardial infarction (MI). METHODS: The cost effectiveness analysis of n-3 PUFA treatment after MI was based on morbidity and mortality data and the use of resources obtained prospectively during the 3.5 years follow-up period of the "GISSI-Prevenzione study" (Lancet 1999), and the Italian cost effectiveness study (pharmacoeconomics 2001). The French patients can be assimilated and compared to the "GISSI Prevenzione" patients & the patients' management and healthcare resources used have been described and validated by an expert panel. Two groups were analysed: treatment with n-3PUFA (n=2836) versus treatment without n-3PUFA (n=2828), the perspective analysis was French NHS (n-3 PUFA - public price: 1 euro per day). RESULTS: The cost effectiveness analysis took into account the incremental number of life years gained (life years gained per patient treated: 0.035) and the incremental cost of hospital admission, diagnostic test and drugs, applying a 2.5% discount. The incremental cost effectiveness ratio for n-3 PUFA in the present scenario was: €18,573 (1999 values). Sensitivity analysis included the analysis of extremes, producing estimates varying from €11,680 to €38,720 euros. CONCLUSION: Since the clinical benefit provided by n-3 PUFA is additive, this therapy should be added to the established routine practice, with additive costs. But even so the cost effectiveness ratio of n-3 PUFA is really reasonable taking into account the threshold considered to be acceptable on an international scale and the other drugs recently introduced in the routine care of secondary prevention after MI.