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A colonoscopy is when a flexible tube is inserted into the anus to view the inside of the large bowel (the colon). This tube transmits film to a screen where signs of any medical condition can be seen.

The colonoscope is a long tube about half the thickness of an electrical cord. It has a camera lens and light so that the bowel can be viewed in detail.

It is flexible and can be turned around corners so it can travel along the length of the large bowel.

At times, it is used to help diagnose conditions. At other times, it is used to treat conditions.

People usually have a colonoscopy:

  • to identify the cause of gut related problems such as abdominal pain or bleeding from the anus
  • if they have a high risk of illness due to chronic bowel disease or a family history of bowel disease such as bowel cancer
  • to identify or remove polyps growing in the lining of the colon
  • to identify or remove bowel cancer


If you are having a colonoscopy, there are a number of steps that need to be followed to get the best result.

The preparations vary between clinics but the aim is to clear the bowel of faeces (poo) so the doctor can get the best view on examination.

The day before the colonoscopy, you may be asked to prepare by drinking a flavoured powder that is mixed with water. This causes diarrhoea to empty the bowel. It's best to do the bowel preparation at home.

The area around the anus may become irritated from diarrhoea. Showering, and using moist wipes instead of toilet paper, may ease this discomfort.

It is important to drink only clear fluids on the day before, and not eat solid foods or dairy products like milk. You will be allowed to have fluids like water, clear fruit juice, clear carbonated drinks and clear soup. You will probably be told to have no fluids in the 6 hours before the colonoscopy.

If you take regular medicine, talk to your doctor. Some medicines should be taken and some can be delayed. It is particularly important to talk to your doctor if you take blood-thinning medicines.

The procedure

The colonoscopy is painless and lasts about 30 minutes. Most people have a mild anaesthetic and can remember nothing or very little. Afterwards, you may feel drowsy, and it is best to arrange somebody to help you get home. Your doctor may give you a brief report on what they saw, but you probably won't get full results and further advice until later at a follow up appointment.

Colonoscopy as a screening test

A colonoscopy is the best way to diagnose bowel cancer and for most people it is a straightforward test. But, as with most medical tests, complications may occur. For this reason, the Royal Australian College of General Practitioners recommend that if you are at average or slightly above average risk of bowel cancer, a faecal occult blood test (poo test) is used for screening rather than a colonoscopy. For more information, visit the Choosing Wisely Australia website.

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Last reviewed: November 2018

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