In view of the rarity of small-bowel epithelial neoplasms as compared with the case for the large bowel, evidence for an adenoma-carcinoma sequence in the small bowel was studied based on a search for data in the medical literature for the years 1927 through 1986. Sufficiently defined data were found for comparison of 185 benign adenomas, 76 adenoma-with-carcinomas, and 1333 carcinomas in patients without familial polyposis disease and for 63, five, and 30, respectively, in patients with disease. For patients without polyposis, it was found that (1) 29.8% of all small-bowel adenomas (33.6% if those at Vater's ampulla are excluded) showed malignancy; (2) the mean and median ages were lower for benign adenoma than for adenoma-with-carcinoma and carcinoma, although the ratios by sex were the same; (3) there is a nearly identical spatial distribution of the three types of epithelial neoplasms within the small bowel; and (4) both the frequency of finding adenomatous residues existing in continuity with carcinoma and the life history of the adenoma-carcinoma sequence are similar in the small bowel as in the large. In comparing these results with those from patients with familial polyposis disease, it was particularly noted that (1) the only difference was that adenomas in familial polyposis occurred earlier and multiply, and (2) the spatial distributions of adenomas and carcinomas for both cases were closely similar. It is therefore postulated that the adenoma-carcinoma sequence is as significant in the small bowels as in the large. A hypothesis regarding the relationship of epithelial neoplasms in people with and without familial polyposis disease is suggested.