Hirschsprung's disease is the most common of a group of related disorders in which there is disruption of the normal mechanisms of colonic transport and defecation, and delay or failure to pass meconium spontaneously. In its more severe forms, Hirschsprung's disease is also the most frequent cause of lower intestinal obstruction in the newborn. Defecation is one of the few essential neuromuscular functions which does not occur normally in utero. Thus while respiratory movements, limb movements, intestinal peristalsis, and passage of urine are present during fetal life, in the normal baby meconium is passed only after birth. Ninety-four per cent of neonates have passed meconium by 24 hours and 99 per cent by 48 hours. Any variance from this pattern may be an early indication of an anorectal neuromuscular abnormality. Although the specific pathogenesis of Hirschsprung's disease remains unclear, there have been continuing advances in both our understanding of the disturbances in bowel motility in this disorder and our means for diagnosing it. With our present knowledge, Hirschsprung's disease should almost always be recognized during the neonatal period. Such earlier diagnoses together with the good long-term results after operative correction provide an excellent prognosis for this illness. Future definition of the etiologic factors responsible for Hirschsprung's disease hopefully may affect an antepartum preventive approach to this disease.