Over a 16-year period 34 patients underwent surgery for idiopathic megarectum or megacolon; 18 had megarectum with or without megasigmoid, one megacolon only and 15 megarectum and total megacolon (nine with a previous colectomy). Ten patients underwent low rectal or anal anastomosis without pouch formation (colodistal proctostomy, eight; coloanal anastomosis, two), eight had colonic pouch-anal anastomosis (J pouch) and 14 had an ileal J pouch after restorative proctocolectomy; one underwent subtotal colectomy with ileorectal anastomosis and one loop ileostomy alone. There was one death, from intestinal obstruction 24 months after operation. Twenty-seven of 32 evaluable patients without a stoma became fully continent following resection and sphincter-saving procedures. Three of 18 had a poor result after resection for megarectum because of recurrent constipation. One of 14 patients became incontinent after restorative proctocolectomy for megacolon and megarectum and in a further four persistent abdominal distension and pain was treated by pouch excision.