By instilling water into the large intestine, sonographic visualization of the whole length of the colon from the rectosigmoid to the cecum can be achieved. Furthermore, using this method, it is possible to evaluate the lumen, the intestinal wall, and the surrounding connective tissue in detail. In our study, severe, active colonic Crohn's disease and ulcerative colitis could be detected by diagnostic sonography of the colon with a sensitivity of 91% and 89%, respectively. Pathological changes were subsequently confirmed by colonoscopy. Differing echo patterns made differentiation of these two diseases possible. Our results thus show that colonic sonography is a diagnostic procedure that promises to greatly facilitate the evaluation and differentiation of inflammatory large bowel diseases.