Between 1986 and 1989, 18,244 men aged 45-64 years in Shanghai, China, participated in a prospective study of diet and cancer. All participants completed an in-person, structured interview and provided blood and urine samples. As of September 1, 1998, 113 deaths from acute myocardial infarction were identified. After analyses were adjusted for age, total energy intake, and known cardiovascular disease risk factors, men who consumed >or=200 g of fish/shellfish per week had a relative risk of 0.41 (95% confidence interval: 0.22, 0.78) for fatal acute myocardial infarction compared with men consuming <50 g per week. Similarly, dietary intake of n-3 fatty acids derived from seafood also was significantly associated with reduced mortality from myocardial infarction. Neither dietary seafood nor n-3 fatty acid intake was associated with a reduced risk of death from stroke or ischemic heart disease other than acute myocardial infarction. However, approximately a 20% reduction in total mortality associated with weekly fish/shellfish intake was observed in the study population (relative risk = 0.79, 95% confidence interval: 0.69, 0.91). These prospective data suggest that eating fish and shellfish weekly reduces the risk of fatal myocardial infarction in middle-aged and older men in Shanghai, China.