Hirschsprung's disease (HSCR) is a congenital disorder characterized by intestinal obstruction due to the absence of intramural ganglia along variable lengths of the colon. Occurrence among family members and recurrence risks among siblings are indications for involvement of genetic predispositions. Mutations have been discovered in five different susceptibility genes. One of the most important findings is the detection of specific mutations in the so-called RET gene, which can also be responsible for the multiple endocrine neoplasia type 2A (MEN2A) syndrome. HSCR patients with such specific mutations run an increased risk of developing MEN type 2A related tumours.