Hirschsprung's disease is marked by constipation from the time of birth, with the development, if uncorrected, of a protuberant abdomen and flared costal margins. The rectal ampulla is empty and the abdomen is filled with fecal masses. Pain is not prominent. Flatus is passed in large amounts. Encopresis does not occur. Barium enema shows the characteristic narrowed distal rectal segment and biopsy of the rectum shows absence of the ganglion cells of the myenteric plexus. Treatment is operative resection of the distal narrow segment and a primary anastomosis.Hirschsprung's disease may be mimicked in children with:1. Psychogenic constipation-pseudo-Hirschsprung's disease. Unlike Hirschsprung's disease, symptoms do not appear at birth, encopresis is common, and the barium enema shows no narrow distal segment.2. Mental retardation and cerebral defect.3. Corrected imperforate anus-on the basis of stenosis, imperfect innervation or poor habit training.4. Cretinism-with severe constipation and intestinal dilatation perhaps the presenting symptoms. Treatment of these four groups of children with severe constipation not due to Hirschsprung's disease is:For Group 1, open discussion with parent and child. Assumption by the physician of full control of the details of treatment, and relegation of parent to the role of the physician's agent in following the prescribed regimen. For Group 2, an enema regimen. Whereas fairly rapid restoration (and then persistence) of normal bowel habit can be expected in Group 1, the basic defects in Group 2 may require indefinite continuation of treatment. For Group 3, regular enema regimen, in the less severe cases-one identical with that used in Group 1, and dilatation of strictures or anoplasty. In Group 4, thyroid hormone therapy relieves the constipation of hypothyroidism and causes reversion of radiographic changes in the colon and rectum.