From 1977 to 1991, we encountered 67 patients with Hirschsprung's disease and 14 of them developed enterocolitis, with 3 cases being fatal. Enterocolitis occurred preoperatively in 12 infants, as well as after ileostomy in one and after a pull-through procedure in another. Seven infants had severe enterocolitis, including three with pseudomembranous enterocolitis and four with hemorrhagic necrotizing enterocolitis. Enterocolitis in Hirschsprung's disease mainly occurs due to intestinal obstruction and ischemia; however, in some cases, Clostridium difficile overgrowth and its toxin also appears to be related to severe pseudomembranous enterocolitis. In severe enterocolitis, antibiotics and enterostomy often prove to be ineffective, and thus an early resection of the affected bowel appears to be necessary. Moreover, when the aganglionic segment extends to the small bowel, severe enterocolitis tends to occur in the aganglionic intestine even after performing an enterostomy, and a resection of the aganglionic bowel is therefore recommended to allow for adequate lavage of the segment distal to the enterostomy site.