Results of 3 previous studies suggest that use of aspirin is related to a reduced risk of endometrial cancer, at least in obese women (body mass index, > or =30 kg/m(2)). Using data obtained in a population-based, case-control study in western Washington State, the authors examined this question. Between 2003 and 2005, 410 women diagnosed with invasive endometrial cancer and 356 controls were interviewed regarding the use of aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs). A history of use of NSAIDs was not associated with the risk of endometrial cancer (odds ratio = 1.04, 95% confidence interval: 0.76, 1.42). The lack of association was also present specifically for use of aspirin (odds ratio = 1.06, 95% confidence interval: 0.73, 1.53). NSAID use was unrelated to risk of endometrial cancer in both obese and nonobese women. Results from this study suggest that the use of aspirin or other NSAIDs has little or no influence on the risk of endometrial cancer.