Histopathologic comparison of colorectal adenomas removed at St. Mark's Hospital, London, England, and those removed at the University of Tokyo, Japan was performed. There were 1242 lesions in the St. Mark's series and 310 in the University of Tokyo series. All adenomas were removed either by colonoscopic polypectomy or hot biopsy. The indications and methods of colonoscopic removal were similar in the two series. Age distribution of the patients showed a younger peak incidence in the University of Tokyo series compared with the St. Mark's patients. The percentage of adenomas larger than 1 cm, of tubulovillous or villous type, and with moderate or severe dysplasia were greater in the St. Mark's series than in the University of Tokyo series. Percentages of adenomas with mild, moderate, or severe dysplasia in each category of size did not differ between the two series. In view of the fact that there is a high colorectal cancer risk in England and medium cancer risk in Japan, our results give further epidemiologic support to the concept of the adenoma-carcinoma sequence.