Most people should have screening for colon cancer at 50 and then every five to 10 years after that, if the first test is normal. By age 75 — if you've always had normal colonoscopies — you can stop taking this test altogether. That should be good news, because a colonoscopy can cause serious complications in older people. “Just the preparation for colonoscopy can be exceptionally harsh,” says UTMB’s Dr. James Goodwin, who studies overuse of colonoscopies. Some patients become incontinent or experience weeks of pain, diarrhea and constipation. In worst cases, the procedure can perforate the colon. Despite such risks, recent studies have found that substantial numbers of people over 75, even over 85, are still getting screening colonoscopies.