Although the small intestine contains 75% of the mucosal surface of the gastrointestinal tract, it is the site of only 2% as many malignancies as the large bowel. The association of Crohn's disease with small intestine adenocarcinoma is well known, but the analytic epidemiology of small intestine malignancies has not received much attention. We reviewed the medical records of 19 patients with adenocarcinoma and 17 with malignant carcinoids identified from the Columbia-Presbyterian Medical Center Tumor Registry in the years 1980-1987. These were compared with 52 controls with nonmalignant conditions from the same time period. Three adenocarcinoma patients but no carcinoid patients or controls had previous Crohn's disease (P < 0.004). Three adenocarcinomas and three carcinoids, but no controls, had previous cholecystectomy (P < 0.004). Previous peptic ulcer disease was recorded for two patients with adenocarcinoma and three with carcinoid but no controls (P < 0.02, P < 0.0002). The age and sex adjusted odds ratio for cigarette smoking was 4.6 (95% confidence interval, 1.0-20.7) for adenocarcinomas and 4.2 (0.8-22.4) for carcinoids. The adjusted odds ratio for alcohol consumption was 4.0 (1.0-15.9) for adenocarcinomas and 3.1 (0.7-13.9) for carcinoids. Further studies are warranted to confirm these associations and to identify potential protective factors in the small intestine.