Hirschsprung's disease (HD) is a relatively common cause of intestinal obstruction in the newborn, characterized by the absence of autonomic ganglion cells in the terminal bowel. Existence of familial cases indicates that genetic factors may be involved in the etiology of some cases of HD. Different inheritance patterns observed in subsets of HD families or kindreds, and the detection of different chromosome aberrations in some HD patients, suggest genetic heterogeneity of HD. Recent expansion of molecular genetics has identified multiple susceptibility genes of HD. These include the RET gene, the glial cell-derived neurotrophic factor gene, the endothelin-B receptor gene, and endothelin-3 gene. Furthermore, some other genes or genetic factors are speculated to be implicated in the development of HD, and it is believed that multiple factors play a role in disease development in some cases. Taken together, these data suggest and may explain the complexity of the etiology of HD. This review focuses on recent advances in our understanding of the genetic aspects of HD.