A woman of 36 was admitted to hospital because of griping abdominal pain which occurred especially during the night when turning in bed. She had a history of constipation and bloating since birth. Irrigoscopy revealed megacolon extending from the middle of the transverse colon to the rectum. A rectal biopsy excluded Hirschsprung's disease. When surgery was performed, megacolon combined with malrotation of the colon was found, only the ascending colon being attached to the abdominal wall. Hemicolectomy was performed. In the megacolon, a cropolith, the size of a foetal head, was found which along with malrotation of the large intestine had caused the woman's symptoms. The nerve supply of the ascending colon was normal but in the megacolon there was evidence of delayed migration of ganglion nerve cells and varying degrees of degeneration of ganglion nerve cells and intraganglionic nerve fibres. Malrotation of the colon associated with megacolon and delayed migration of ganglion nerve cells and degeneration of nerve elements has not been reported previously.