Vitamin D and its analogues exhibit potent antitumor effects in many tissues, including the pancreas. Normal and malignant pancreatic tissues were recently shown to express high levels of vitamin D 1-alpha-hydroxylase, which converts circulating 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D. We examined associations between dietary intake of vitamin D, calcium, and retinol and subsequent risk for pancreatic cancer. We conducted prospective studies in cohorts of 46,771 men ages 40 to 75 years as of 1986 (the Health Professionals Follow-up Study), and 75,427 women ages 38 to 65 years as of 1984 (the Nurses' Health Study), documenting incident pancreatic cancer through the year 2000. Diet was ascertained by semiquantitative food-frequency questionnaire. We identified 365 incident cases of pancreatic cancer over 16 years of follow-up. Compared with participants in the lowest category of total vitamin D intake (<150 IU/d), pooled multivariate relative risks for pancreatic cancer were 0.78 [95% confidence interval (95% CI), 0.59-1.01] for 150 to 299 IU/d, 0.57 (95% CI, 0.40-0.83) for 300 to 449 IU/d, 0.56 (95% CI, 0.36-0.87) for 450 to 599 IU/d, and 0.59 (95% CI, 0.40-0.88) for >/=600 IU/d (P(trend) = 0.01). These associations may be stronger in men than women. After adjusting for vitamin D intake, calcium and retinol intakes were not associated with pancreatic cancer risk. In two U.S. cohorts, higher intakes of vitamin D were associated with lower risks for pancreatic cancer. Our results point to a potential role for vitamin D in the pathogenesis and prevention of pancreatic cancer.