Laboratory studies indicate that nonsteroidal anti-inflammatory drugs (NSAIDs) may inhibit pancreatic cancer, but epidemiologic data to support this finding are limited. We conducted a prospective study from 1992 through 1999 among 28 283 postmenopausal women who lived in Iowa to examine the association between the self-reported use of aspirin and other NSAIDs and the incidence of pancreatic cancer. Eighty incident cases of pancreatic cancer were identified during 7 years of follow-up. The multivariate-adjusted relative risk of pancreatic cancer associated with any current use of aspirin versus no use was 0.57 (95% confidence interval = 0.36 to 0.90). There was a trend of decreasing risk of pancreatic cancer incidence with increasing frequency of aspirin use per week (P(trend) =.005). Nonaspirin NSAID use was not associated with incident pancreatic cancer. These data indicate that aspirin might be chemopreventive for pancreatic cancer.