Depressed adenomas of the colon have been reported more often during the past several years, but there are few reports on the details of their characteristics or behavior. In this study, depressed and ordinary polypoid adenomas, especially those in an early stage, in the large intestine of 28 patients with familial adenomatous polyposis (FAP) were examined macroscopically, by dissecting microscope, and histologically. Proliferating cell nuclear antigen (PCNA) and the density of crypts in the background mucosa around depressed and polypoid adenomas were also compared. Depressed adenomas of < 1.0 mm in diameter showed horizontal growth between the normal adjacent crypts, which often left the normal crypts as islands, whereas polypoid adenomas grow expansively without including remnants of normal crypts. In depressed adenomas, PCNA shifted to the upper part of the crypts, and the background mucosa in their vicinity showed a low density of crypts. These findings indicate that a unique characteristic of growth of depressed adenomas at an early stage is superficial proliferation.