Objectives: To review all prospective cohort studies examining the relationship between fish intake and coronary heart disease mortality, and to assess the strength and consistency of their findings. Design: Systematic review of studies based on individual records of fish or n-3 polyunsaturated fatty acid consumption and coronary heart disease death. Studies were given scientific quality scores and divided into categories of high, intermediate, or insufficient quality. Main outcome measure: Coronary heart disease mortality. Results: Eleven studies were identified. The cohorts counted a total of 116,764 individuals. Of four studies judged to be of high quality, the two largest (n = 44,895 and 20,051) were performed in populations at low risk of coronary heart disease. They found no protective effect of fish consumption. The other two high-quality studies were relatively small (n = 852 and 1822) and included individuals at higher risk. They both found an inverse relationship between fish consumption and coronary heart disease death, suggesting that 40-60 g fish per day is optimal and associated with a risk reduction of 40-60%. Results of four studies of intermediate quality support that fish consumption is inversely associated with coronary heart disease mortality in high-risk populations only. Three studies were judged to be of insufficient quality to be used for drawing conclusions. Conclusions: Fish consumption is not associated with reduced coronary heart disease mortality in low-risk populations. However, fish consumption at 40-60 g daily is associated with markedly reduced coronary heart disease mortality in high-risk populations. The underlying biochemical mechanism is nor known and causal inference premature.