MUNAKATA, A., NAKAJI, S., TAKAMI, H., NAKAJIMA, H., IWANE, S. and TUCHIDA, S. Epidemiological Evaluation of Colonic Diverticulosis and Dietary Fiber in Japan. Tohoku J. Exp. Med., 1993, 171(2), 145-151 - The incidence of colonic diverticulosis was examined in 5 hospitals geographically isolated from each other in Japan during the period between mid '70s and 1986. The incidence rapidly increased in all hospitals from 3.5-9.0% in mid '70s to 8.4-23.2% in 1986. The ratio of right-sided type colonic diverticulosis was approximately 70-80% in each hospital and the ratio did not fluctuate significantly during the period. Birth cohort analysis revealed that although the incidence of right-sided diverticula had increased with aging, in groups born in more recent decades right-sided diverticula appeared in younger age than other groups. It was suggested that environmental factors rather than congenital factors may cause the increase of the incidence of right-sided colon diverticula.