The growth type of early colorectal carcinoma was classified into two types. The first type is intramucosal polypoid growth (PG-Ca) and the second type nonpolypoid growth (NPG-Ca) which shows mainly massive infiltration of tumor cells below the submucosal layer. The incidence of adenoma-carcinoma sequence was 72 of 75 lesions (96.0%) in pedunculated polypoid carcinoma, and 61 of 71 lesions (85.9%) in sessile and broad-based polypoid carcinomas. Their average sizes were 15.0 and 18.7 mm, respectively. Submucosal invasive carcinoma (SM-Ca) showed a low incidence. They were detected as microscopical or scattered lesions with a few lymphatic and venous permeation. The NPG-Ca contained 32 lesions. Intramucosal carcinoma without adenoma showing slight depression consisted of ten lesions of which the average size was 5.1 mm. The other 22 lesions showed massive submucosal invasion with marked lymphatic and venous permeation. The average size was 10.3 mm being smaller than PG-Ca. Histologically, NPG-Ca was not accompanied with adenoma. The NPG-Ca arose from de novo carcinoma less than 10 mm in diameter and invaded into the submucosal layer. In advanced carcinoma, the PG-Ca showed a low incidence (21.8%), and almost all cases were of the NPG type (78.2%). The NPG advanced carcinomas increased in those over the size of 20 mm. It is concluded that nonpolypoid early colorectal carcinomas easily progress to advanced carcinoma, and de novo carcinoma occupied about 80% of colorectal carcinoma.