The consumption of fatty fish, which contains large amounts of omega-3 fatty acids, may lower the risk of hormone-responsive cancers. Our aim was to study the association of fish consumption and endometrial cancer risk in Sweden, a country with a wide range of high fatty fish consumption. Using data from a large, nationwide case-control study (709 cases and 2888 controls), we analyzed consumption of both fatty (e.g., salmon and herring) and lean (e.g., cod and flounder) fish in relation to endometrial cancer risk, adjusting estimates for a wide range of potentially confounding variables. Odds ratios (ORs) and 95% confidence intervals (CIs) were computed from unconditional logistic regression models fit by maximum likelihood methods. Consumption of fatty fish was inversely associated with endometrial cancer risk. The multivariate OR for women in the highest quartile level (median, 2.0 servings per week), compared to women with in the lowest (median, 0.2 servings per week), was 0.6 (95% CI, 0.5-0.8; P for trend, 0.0002). The corresponding OR for women in the highest quartile level of lean fish (median, 2.5 servings per week), compared to women in the lowest (median, 0.6 servings per week), was 1.0 (95% CI, 0.8-1.3; P-value for trend, 0.72). Total fish consumption was inversely associated with risk, although weakly. Our results suggest that the consumption of fatty fish, but not other types of fish, may decrease the risk of endometrial cancer.