The results of the Duhamel operation in patients with idiopathic megarectum and megacolon have been reviewed. Twenty patients (14 males, six females) underwent the Duhamel operation over a 17-year period for this condition. The mean age at operation was 25 years; the mean age of onset of constipation was 3 years; and the mean follow-up period was 4.5 years. All the resected colons were of enlarged diameter. There was agreement between the preoperative radiographs and the operative specimens with regard to which parts of the rectum and colon were dilated. Subjective feelings of well-being were generally improved by surgery, as was bowel frequency in ten patients. Soiling, straining, abdominal pain and distension were, however, common after operation. Early complications were also common and five patients required further surgery for constipation. The Duhamel operation for megarectum and megacolon is characterized by an improved sense of well-being and improved bowel frequency, but it is associated with the persistence of many symptoms and further surgery is often required.