摘要Dilatation of the colon and the rectum, which is not attributable to aganglionosis, is a rare finding and can be the result of intractable chronic constipation. We report a rare case of a 29-year-old male patient with impressive megacolon, in whom Hirschsprung's or Chagas disease was ruled out. In the present case, dilatation of the colon was most likely due to a behavioral disorder with habitual failure of defecation. Chronic stool retention led to a bizarre bulging of the large bowel with displacement of the other abdominal organs and severe occult blood loss. Because of two episodes of life-threatening gastrointestinal bleeding despite conventional treatment of constipation, a surgical approach for bowel restoration was necessary. Temporary loop ileostomy had to be performed for depressurization of the large bowel and the subsequent possibility for effective antegrade colonic lavage to remove impacted stools. Shortly after the operation, the patient was healthy and could easily manage the handling of the ileostomy. However, the course of the megacolon in this young adult cannot be predicted and the follow-up will have to reveal if regression of this extreme colonic distension with reestablishment of regular rectal perception will occur.