We report an autopsied 20-year-old man case of intestinal necrosis associated with megacolon from hypoganglionosis, a pseudo-Hirschsprung's disease. The patient had suffered from severe constipation since two years of age, and presented abdominal distention from age ten. Autopsy revealed marked dilatation and necrosis of the entire large intestine. Although ganglion cells in the intestinal plexus were found throughout the large intestine, their number was reduced to 12-20% of that in the normal control. In pseudo-Hirschsprung's disease, there are occasional cases where an acute abdomen first presents itself in adulthood after running its course as chronic constipation.