The association of gallbladder and bile duct cancers with gallstones, cholecystitis, and cholangitis suggest that chronic inflammation contributes to the carcinogenic process. However, the effect of nonsteroidal anti-inflammatory drugs, such as aspirin, on biliary tract cancer has not been well studied. In a population-based case-control study conducted in Shanghai, China, we examined the relationship between aspirin use and the risk of biliary disease. A total of 627 patients with biliary tract cancer, including cancers of the gallbladder (n = 368), extrahepatic bile duct (n = 191), and ampulla of Vater (n = 68); 1,037 patients with biliary stones; and 958 healthy adults were included in the study. Self-reported data on aspirin use was collected from study participants by in-person interview. The prevalence of aspirin use was low, with 5.7% of the population controls being regular users. After controlling for age, sex, education, and biliary stone status, aspirin use was associated with a reduced risk of gallbladder cancer [odds ratio (OR), 0.37; 95% confidence interval (CI), 0.17-0.88]. An inverse relationship was also observed for frequency and duration of use and with younger age when starting use. In addition, there was a nonsignificant reduction in the risk of bile duct (OR, 0.48; 95% CI, 0.19-1.19) and ampullary cancers (OR, 0.22; 95% CI, 0.03-1.65) associated with aspirin use, whereas no clear association was seen with biliary stones (OR, 0.92; 95% CI,