Malignant neoplasms of the small intestine are relatively rare and have received little study. We report on trends in the age-adjusted, sex-, and race-specific incidence rates of adenocarcinomas and carcinoid tumors of the small intestine in the United States from 1973 through 1991. Data were derived from the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute. There were statistically significant increases in the incidence rates of both adenocarcinomas and carcinoid tumors during the time frame of the study. Rates increased most dramatically in black males, with 2- and 4-fold increases in adenocarcinomas and carcinoid tumors, respectively. The only rates that remained relatively unchanged were those of adenocarcinoma among white females. It remains to be determined if changing environmental factors are important causes of these observed trends. If environmental factors are involved in the etiology of small intestine cancers, analytic studies conducted while the disease is increasing in incidence may provide useful insights.