A colonoscopy is a test that lets your doctor look all the way inside your large intestine, also called your colon.

It uses a thin, flexible tube called a colonoscope.

The scope has a tiny light and video camera on the end and is connected to a computer screen.

A colonoscopy is one of a few tests used to screen for colon cancer.

A doctor may be able to find cancer early or find colon polyps.

A polyp is a small growth of excess tissue.

Some types of colon polyps can lead to cancer.

The test can also be used to find the cause of problems like diarrhea, intestinal or rectal bleeding, or belly pain.

But before the test can be done, you have a really important job to do.

You need to clean out your colon.

This is usually called colon prep.

Be sure to follow your doctor's instructions.

If you don't do a good job preparing your colon, the test may not be good enough.

And you may have to do it all over again.

Here's how the test is done.

Just before the test, you'll be given a medicine that will make you sleepy and help with any discomfort.

Because of the medicine, you probably won't remember what happens during the test, and you'll need to make sure you have someone to take you home once the test is done.

During the test you'll lie on your side with your knees pulled up.

Your doctor will gently put a gloved finger into your anus and then gently slide the colonoscope into your anus so it can be moved slowly through all the parts of your colon.

Your doctor may take tissue samples or remove some polyps during the test.

The test usually takes less than an hour.