17 patients with colonic diverticulitis of various degree were examined by conventional abdominal ultrasound in comparison to either colonoscopy or operation. The sonography of the inflammated region showed an echo-poor enlargement of the colonic wall (normal less than 3 mm) ranging from 5 to 15 mm (mean 7.8 mm) over a short distance. In cases with bowel wall enlargement of more than 11 mm a spontaneous evacuation of pus from the diverticles was endoscopically seen. A sonographic enlargement of the colonic wall of more than 15 mm is very suspicious to be a peridiverticulitis or a beginning abscess. In two patients we were able to show single inflammated diverticula by sonography. Thus ultrasonography seems to be an important noninvasive method to diagnose diverticulitis including the complications (perforation, abscess or fistulation) as well as to control the success of conservative treatment.