This is an examination of the whole of the large bowel (colon) through your back passage. It is carried out by (or under direct supervision of) a trained doctor or nurse called an endoscopist. A colonoscopy is a very accurate way of looking at the lining of your large bowel to establish whether there is any disease or abnormality present.
The instrument used is called a colonoscope (scope) and is a thin flexible tube. The scope has a light which is shone in to the lining of you large bowel. It also has a very small camera which sends live images to a screen where it is viewed by the endoscopist as the scope is negotiated around your large bowel to the caecum.
During the procedure, the endoscopist may need to take some small tissue samples called biopsies for analysis; this is painless. They may also take some photographs to retain in your medical records.