The enterocolitis associated with Hirschsprung's disease (HD) has not been clearly characterized. This study was undertaken to analyze the clinical and radiological findings of Hirschsprung's enterocolitis (HEC) in 168 patients treated from July 1974 through October 1992. HEC occurred in 57 patients (33.9%), either preoperatively (13; 7.7%) or postoperatively (36; 21.4%). In eight patients (4.8%), it occurred pre- and postoperatively. The number of bouts of HEC per patient ranged from one to six (mean, 2.2). The major presenting features were abdominal distension (83%), explosive diarrhea (69%), vomiting (51%), fever (34%), lethargy (27%), rectal bleeding (5%), and colonic perforation (2.5%). There were no deaths directly related to HEC. The analysis of 150 plain x-rays of the abdomen, taken at the onset of HEC or in between bouts, showed that colonic dilatation was the most sensitive radiological finding (90% sensitivity), but it had poor specificity (24%). However, an intestinal cutoff sign (gaseous intestinal distension with abrupt cutoff at the level of the pelvic brim) was both sensitive (74%) and specific (86%) for HEC. Barium enema was of limited value in the diagnosis of HEC bouts because most of the radiographic findings persisted for prolonged periods after cessation of such bouts. The authors conclude that (1) HEC can be characterized as abdominal distension and explosive diarrhea associated with the intestinal cutoff sign and (2) the occurrence of explosive diarrhea in any patient with HD is suggestive of HEC, even in the absence of systemic symptoms, and should be treated to avoid the morbidity and potential mortality of HEC.