A colonoscopy is a medical test that doctors use to look at the inside of your large intestine (also called your colon). They use a long, flexible tube called a colonoscope. It has a tiny camera and a light on the end that sends pictures of your intestine to a computer. The doctor can check for any illness or growths and take samples of tissue if needed. To do the test, you need to drink special liquids and take medicine to help clean out your intestines so the doctor can get a good look.