We have studied the anatomic distribution of 784 small bowel carcinomas and have analyzed available epidemiologic data to determine the relation of these rare cancers to other gastrointestinal tumors and to diet. The anatomic distribution of small bowel cancer in unusual: most tumors occur in the duodenum or proximal jejunum, relatively few tumors occur in the central bowel, and only in the lower ileum do the expected number of tumors appear. Review of available epidemiologic data shows a correlation between small bowel cancer and lower, but not upper gastrointestinal cancer. The incidence of small bowel cancer is positively correlated with protein and fat consumption.