A colonoscopy is a procedure that allows your healthcare provider to look inside the large intestine, from the rectum all the way up through the colon to the lower end of the small intestine. This procedure is used to check for early signs of colon and rectum cancer and also to determine the cause of unexplained changes in bowel habits. During the colonoscopy, a long, flexible, lighted tube is inserted into your rectum and slowly guided into your colon. If anything abnormal is found, like a polyp or inflamed tissue, it is removed using tiny instruments passed through the scope.