Forty‐five juvenile polyps were found among approximately 390 mucosal polyps of the large Intestine. Various degrees of epithelial pseudostratlflca‐tion were found among juvenile polyps and the larger‐sized polyps of both juvenile type and adult one fended to have a more advanced degree of epithelial pseudostratincation. The glands of both juvenile polyps and adult ones revealed a closely resembled or almost identical pattern of size‐distribution‐pattern of the glandular size in both normal mucosae and hyperplastic mucosae of long‐standing ulcerative colitis. Transition of juvenile polyps into adult ones was suggested by the cases with increase in numbers of glands and their orifices to the surface of the polyp and there were some polyps showing an intermediate form between juvenile polyps and adult ones. On the basis of histologic characteristics and age incidence of the patients, it may be said that a juvenile polyp is an immature variant of an adult polyp. ACTA PATH.