PURPOSE: To evaluate ultrasonographic (US) findings of right-side colonic diverticulitis and to correlate them with pathologic findings. MATERIALS and METHODS: Twenty nine patients with surgically (n=17) and radiographically (n=8) proven diverticulitis in the cecum and ascending colon for the past five years were included in this study, and they all underwent US due to right lower quadrant abdominal pain. US findings were analyzed by two radiologists with a special emphasis on: (1) the presence, size, and internal echo of hypoechoic lesion bulging out from the colonic wall (thickened diverticulum), (2) changes in the adjacent cecum and ascending colon, (3) changes in the adjacent mesentery, (4) accompanying fluid collection, and (5) the presence of lymphadenopathy. US findings of 18 surgically proven patients were correlated with pathologic findings. RESULTS: On US, 25 of 29 patients (86.2%) were found to have thicken diverticulum with the greatest dimension of 8 -20 mm(mean, 12 mm). Wall thickening of the adjacent cecum and ascending colon was seen in 28 patients (96.5%), and 22(75.9%) of them had eccentrically thickened wall. Comparing US findings with pathologic findings in 18 surgically proven patients, all revealed to have inflamed diverticulum on surgery, but only 15 showed thickened diverticulum on US. In 12 patients, fecalith, purulent exudates, and hemorrhage were found within diverticulum on surgery. In cases of diverticulitis containing fecalith, all of their echogenecities were increased. All patients showed wall thickening of the adjacent colon and increased echogenecity of the adjacent mesentery on US. Pathologic findings of these thickend walls contained nonspecific inflammatory change and hemorrhage while the mesenteriy with an increased echogenecity contained purulent or hemorrhagic exudates. CONCLUSION: Ultrasonography can diagnose the right-side colonic diverticulitis when there is the presence of thickened diverticulum in the area with the thickened right side colonic wall in patients with right lower quadrant abdominal pain.