We report a case of fatal Hirschsprung's disease (HD) discovered at autopsy. A 20-year-old man collapsed at home. Emergency medical personnel found him in cardiac arrest and all resuscitative efforts failed. He had a past history of chronic constipation since infancy. Forensic autopsy revealed a megacolon full of gas and stools. Microscopic examination showed absence of ganglion cells in a short segment of the rectum and enterocolitis in the left and transverse colon. HD is rarely described in adults. In many cases, patients complained of constipation since infancy but the affection remained misdiagnosed. The relative good tolerance of the disease is usually due to a short aganglionic bowel segment. Enterocolitis is a frequent and severe complication of HD in children but is rarely described in adults. This case suggests the importance of HD diagnosis in childhood in order to avoid fatal complications with forensic consequences.