Colorectal cancer screenings should start at age 45 for those at average risk, says the American Cancer Society. This can be done with colonoscopy every 10 years, flexible sigmoidoscopy every five years, or stool-based tests like the fecal immunochemical test each year. People at higher risk, such as those with a strong family history, certain polyps, inflammatory bowel disease, or familial adenomatous polyposis, may need screening before age 45. After surgery to remove colon or rectal cancer, a colonoscopy is needed within a year. People with ulcerative colitis or Crohn's disease should get a colonoscopy every one to two years. Prior radiation treatment to the abdomen or pelvis to treat a previous cancer may increase the need for earlier or more frequent colonoscopies. Read more at http://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/acs.