An Ii-month-old girl with a prolonged history of bloody, mucoid diarrhea is presented, Although the initial diagnosis given by the rectosigmoid biopsy obtained during laparotomy was neuronal intestinal dysplasia, accompanying findings including mixed inflammatory cell infiltration of the mucosa and submucosa with mucosal ulcerations suggested nonspecific colitis. The subsequent biopsy specimen that was obtained after performing colostomy and treating with broad-spectrum antibiotics and rectal irrigations showed improvement in the structure of ganglion cells and submucous and myenteric plexuses. Although the mucosal ulcerations and inflammatory reaction improved, the colonic stricture persisted, so the Duhamel procedure was performed, and the patient had an uneventful outcome. It is claimed that inflammatory disease of the rectosigmoid colon of unknown etiology and neuronal intestinal dysplasia have occurred together in the current case or that one disease might cause the other in time. Copyright (C) 2000 by W.B. Saunders Company.