OBJECTIVES Data on small bowel cancers are scarce, and are derived primarily from hospital series. Our aim was to examine the epidemiological and clinical characteristics of these rare cancers. The database is population-based registry with complete ascertainment. It is thus free of the selection bias innate to hospital series. METHODS Review of the Utah Cancer Registry for all small bowel cancers from 1966 through 1990. For comparison, other cancers were reviewed for incidence and relative survival rates. RESULTS There were 328 small bowel cancers, including 136 (41%) carcinoids, 80 (24%) adenocarcinomas, 72 (22%) lymphomas, 36 (11%) sarcomas, and four (1%) unclassified. The overall age-adjusted incidence per 100,000 was 1.4 for small bowel cancers compared to 35.7 for colorectum and 92.9 for breast. Small bowel cancers occurred most frequently in the sixth and seventh decades of life, and were more common in men. Carcinoids, lymphomas, and sarcomas occurred in order of decreasing frequently in the ileum, jejunum, and duodenum; the reverse was true for adenocarcinomas. Distant metastases occurred in 35 (27%) carcinoids, 14 (28%) adenocarcinomas, 17 (26%) lymphomas, and 10 (33%) sarcomas. Surgery was the primary form of therapy in 108 (79%) carcinoid patients, 80 (49%) adenocarcinoma patients, 52 (72%) lymphoma patients, and 26 (72%) sarcoma patients. The overall 5-year relative survival rate for small bowel cancers was 54%; 83% for carcinoids, 25% for adenocarcinomas, 62% for lymphomas, and 45% for sarcomas. Overall survival, compared to other cancer sites, was surpassed only by cancers of the prostate, breast, and colorectum. CONCLUSIONS Small bowel cancers consist of several types of rare tumors, each with unique characteristics. The overall prognosis is better than for most common cancers.