PURPOSE: To investigate the CT findings of acute right colonic diverticulitis, and to determine the differencebetween these and published reports deseribing left colonic, especially sigmoid, diverticulitis. MATERIAL AND METHODS: In 13 patients with acute right lower quadrant pain who underwent ultrasonography a normal appendix wasdemonstrated and acute right colonic diverticulitis was suspected. CT was performed within 24 hours and thefindings were analysed by two radiologists. For further confirmation of diverticulitis, follow-up barium enemaswere performed in ten patients. RESULTS: Inflamed diverticula were visible in all cases, and were solitary. Ninecases occured in the ascending colon and four in the cecum; in particular, eleven occurred around the ileocecalvalve. In three cases, the inflamed diverticulum was less than 1cm in diameter;in five cases, 1-2cm;in three,2-3cm, and in two, 3-4cm. These were able to be classified into two major forms. In three cases it was nodularwith hyperattenuation and some inhomogeneity, and ten shows the target form with thick walls and a central cavity.In five of these target lesions, the wall pattern was partially or completely inhomogenous, or multilayered. Thematerials filling the central cavity were gas in five cases, fecalith in two, and fluid in three. Abnormalpericoloic fat infiltrations were seen in twelve cases(92%), segmental colonic wall thickening in eleven(85%),other not-inflamed diverticula in five(38%), mesenteric lymph node enlargement in three(23%), free pericecal fluidcollection in three(23%), and perirenal fascial thickenings in two(15%). The complications such as remote abscesscavity, colonic obstruction, fistula or perforation were not found. On barium colon study, diverticulitis was inall cases confirmed by the presence of barium in the deformed diverticulum. CONCLUSION: Among CT findings foracute right colonic diverticulitis, the most important and pathognomonic is inflamed diverticula; the forms ofthese vary, and include gangrenous diverticulitis. The CT findings of early right colonic diverticulitis inKoreans might not, however, reveal the complications which sigmoid diverticulitis frequently involves; in patientswith right lower quadrant pain imaging studies are performed promptly, and for the mesentery, the anatomical basebetween right and left colons is different.