The epidemiological patterns for pancreatic and biliary cancers reveal more differences than similarities. Pancreatic carcinoma is common in western countries, although 2 Polynesian groups (New Zealand Maoris and native Hawaiians) have the highest rates internationally. In the United States the disease is rising in frequency, predominating in males and in blacks. The rates are elevated in urban areas, but geographic analysis uncovered no clustering of contiguous counties except in southern Louisiana. The origin of pancreatic cancer is obsure, but a twofold increased risk has been documented for cigarette smokers and diabetic patients. Alcohol, occupational agents, and dietary fat have been suspected, but not proven to be risk factors. Except for the rare hereditary form of pancreatitis, there are few clues to genetic predisposition. In contrast, the reported incidence of biliary tract cancer is highest in Latin American populations and American Indians. The tumor predominates in females around the world, except for Chinese and Japanese who show a male excess. In the United States the rates are higher in whites than blacks, and clusters of high-risk counties have been found in the north central region, the southwest, and Appalachia. The distribution of biliary tumors parallels that of cholesterol gallstones, the major risk factor for biliary cancer. Insights into biliary carcinogenesis depend upon clarification of lithogenic influences, such as pregnancy, obesity, and hyperlipoproteinemia, exogenous estrogens, familial tendencies, and ethnic-geographic factors that may reflect dietary habits. Noncalculous risk factors for biliary cancer include ulcerative colitis, clonorchiasis, Gardner's syndrome, and probably certain industrial exposures. Within the biliary tract, tumors of the gallbladder and bile duct show epidemiological distinctions. In contrast to gallbladder cancer, bile duct neoplasms predominate in males; they are less often associated with stones and more often with other risk factors. In some respects, bile duct and pancreatic tumors are alike. The male predominance of both tumors, an association between cholecystectomy and pancreatic cancer, and other considerations have prompted the notion that the same biliary carcinogens may affect the bile duct, ampulla of Vater, or, by reflux, the pancreatic duct. Various epidemiological and interdisciplinary approaches are needed to further clarify the origins of biliary tract and pancreatic cancers, but nutritional studies hold special promise in laying the groundwork for prevention of these tumors.