Certain polyphenols inhibit the activity of aromatase, a critical enzyme in estrogen synthesis that is coded by the CYP19A1 gene. Consumption of polyphenol-rich foods and beverages, thus, may interact with CYP19A1 genetic polymorphisms in the development of endometrial cancer. The authors tested this hypothesis in the Shanghai Endometrial Cancer Study (1997-2003), a population-based case-control study of 1,204 endometrial cancer cases and 1,212 controls. Dietary information was obtained by use of a validated food frequency questionnaire. Genotypes of CYP19A1 at rs28566535, rs1065779, rs752760, rs700519, and rs1870050 were available for 1,042 cases and 1,035 controls. Unconditional logistic regression models were used to calculate odds ratios and their 95% confidence intervals after adjustment for potential confounding factors. Higher intake of soy foods and tea consumption were both inversely associated with the risk of endometrial cancer, with odds ratios of 0.8 (95% confidence interval: 0.6, 1.0) for the highest versus the lowest tertiles of intake of soy and 0.8 (95% confidence interval: 06, 0.9) for ever tea consumption. The association of single nucleotide polymorphisms rs1065779, rs752760, and rs1870050 with endometrial cancer was modified by tea consumption (p(interaction) < 0.05) but not by soy isoflavone intake. The authors' findings suggest that tea polyphenols may modify the effect of CYP19A1 genetic polymorphisms on the development of endometrial cancer.