Sonographic findings in 16 patients with diverticulitis of the colon are described. The wall of the inflamed segment of the colon appeared hypoechoic and thickened. Maximum thickness of the wall ranged from 5 to 17 mm. Length of the most severely inflamed segment of the colon ranged from 6 to 9 cm. In addition, adjacent contiguous segments of the colon, less involved with inflammation, ranging in length from 7 to 15 cm, were demonstrated on sonographic examination of five patients. Long segments of the inflamed colon could be demonstrated by oblique scanning. The appearance of the mucosal reflections, intramural abscesses, and inflamed diverticula is described. Out of 16 patients with diverticulitis, seven patients had abscesses and extravasation of barium was seen in only two of these seven patients. Ultrasonography therefore is recommended prior to barium or water-soluble contrast enema examination in patients with suspected diverticulitis. In patients with appropriate clinical findings, sonographic diagnosis of diverticulitis can be made by demonstrating hypoechoic thickening of the wall of the colon, even in the absence of intramural or intraperitoneal abscess.