Megacolon is a condition that is not uncommon in the cat. Most cases are idiopathic (a cause cannot be determined), and these seem to be a result of colonic inertia. Pelvic fracture malunions are the next most common cause and result in a pelvic outlet obstruction. Total or subtotal colectomy offers good long-term results in cases of idiopathic megacolon and chronic cases of pelvic fracture malunion, and the technique is described in detail.