SummaryAbnormally shaped arteries were found in the intestines of 17 of 62 patients (27%) with Hirschsprung's disease. The histological characteristics of abnormal arteries included proliferation of collagen fibers and smooth muscle cells in the adventitia. The incidence of abnormal arteries in each type of aganglionosis was as follows: 25% (13 of 51) in short-segment aganglionosis; 0% (0 of 6) in long-segment aganglionosis; and 80% (4 of 5) in totalcolon or extensive aganglionosis. The older the patients were at the time of resection, the higher the incidence of abnormal arteries (<1 year old, 15%; 1–3 years old, 38%; >3 years old, 75%). The abnormally shaped arteries were mostly located in the histological transitional zone. These findings suggest the following possibilities: (a) the craniocaudal migration of ganglion cells was interrupted by intestinal ischemia in the presence of abnormal arteries in utero; (b) an ischemic episode caused both the disappearance of neural cells and dysplasia of the artery; (c) the ganglion cells were destroyed by mild ischemia caused by the abnormal arteries; or (d) the tension caused by mechanical expansion resulted in a change in the vascular walls in the transitional zone.