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Location, size and histological appearance of colorectal neoplasms were examined retrospectively. A total of 1,357 polyps (including small ones, diameter below 0.5 cm) were found in 1,022 of 3,057 coloscopies. The coloscopies were indicated by findings on preceding radiological or endoscopic examinations (48%), occult blood in stool (18%), during follow-up after polypectomy (21%), and after colorectal carcinoma (13%). A single polyp was found in 718 cases (70%), two to four in 221 (26%), more than five in 33 (4%), 1,106 polyps (61%) were found on high coloscopy; 380 of these (38%) were located proximal to the left flexure. Among the 1,230 polyps examined histologically 907 (74%) were adenomas (494 tubular [54%], 379 tubulovillous [42%], 34 villous [4%]). 251 (28%) of the adenomatous polyps and 49 (32%) of the 151 carcinomas were located proximal to the left flexure. The incidence of moderately severe to severe dysplasias increased with increasing diameter of the polyps: 55% of those smaller than 0.5 cm were adenomas. 70% of polyps with a diameter over 1.0 cm were tubulovillous or villous adenomas. The findings confirm that there is a high incidence of polyps proximal to the left flexure. A complete coloscopy should therefore be done as a matter of course.