Individuals with an average risk for colon cancer should have their first colonoscopy at age 50 and every 10 years thereafter, reports the American Cancer Society. Those with a family history of colon cancer should undergo colonoscopy at age 40 and every five years after the initial procedure.
If colon polyps were found on a previous colonoscopy, the size of the polyp determines the interval between procedures, notes the American Cancer Society. Adenomas less than 1 centimeter in size warrant a repeat colonoscopy five to 10 years after diagnosis, while adenomas larger than 1 centimeter require a repeat procedure within three years.
Conditions that warrant a colonoscopy before the age of 50 include ulcerative colitis and Crohn's disease, according to WebMD. Individuals with a family history of colon cancer or colon polyps before the age of 60 and those with a history of familial adenomatous polyposis should also undergo a colonoscopy before the age of 50.