Colonoscopy is a test that allows your doctor to look at the interior lining of your large intestine (rectum and colon). A colonoscopy is done using a thin, flexible viewing instrument called a colonoscope.
Colon polyps usually do not cause symptoms unless they are larger than or they are cancerous. The most common symptom is rectal bleeding. Sometimes the bleeding may not be obvious (occult) and may only be discovered after doing a screening test.