The distinction between Hirschsprung's disease and idiopathic megacolon in childhood dates from the classic clinical, radiological, and histological studies of Bodian, Stephens, and Ward. This article describes clinical experience over 15 years of 94 patients in whom megacolon of these two types was recognised for the first time after the age of 10, to illustrate the problems of diagnosis and treatment in later years. Just as it is now recognised that patients with the clinical characteristics of Hirschsprung's disease may have one of several abnormalities of the myenteric plexus, including not only absence of ganglion cells, but also patchy or zonal loss, abnormal neurones or neuronal dysplasia, so idiopathic megacolon may also be a heterogeneous group of cases. This paper suggests on clinical grounds that those patients with idiopathic megacolon whose symptoms start in childhood differ from those whose symptoms develop in later years.