In cats, clinical signs of constipation usually respond to laxatives, fecal softeners, enemas, and dietary management. Uncommonly, constipation is chronic and is associated with a marked increase in the diameter of the colon. When megacolon is present, constipation responds poorly to medical therapy. Without surgical treatment, megacolon may become an intolerable problem, with euthanasia of the cat as the probable outcome. Subtotal colectomy is now established as a satisfactory treatment for idiopathic megacolon in cats. Recently, removal of the colon has been used successfully to treat chronic constipation and megacolon associated with mechanical obstruction of the pelvic canal caused by stenosis from malunion of pelvic fractures. Colectomy has minimal long-term effects on enteric function in cats.