Colonoscopy and sigmoidoscopy are procedures that let your doctor look inside your large intestine. They use instruments called scopes. Scopes have a tiny camera attached to a long, thin tube. The procedures let your doctor see things such as inflamed tissue, abnormal growths, and ulcers.
Colonoscopy checks your entire colon and rectum. Sigmoidoscopy checks the rectum and the lower colon only.
Your doctor may recommend one of these procedures
- To look for early signs of cancer in the colon and rectum. It may be part of a routine screening, which usually starts at age 50.
- To look for causes of unexplained changes in bowel habits
- To evaluate symptoms like abdominal pain, rectal bleeding, and weight loss
Your doctor can also remove polyps from your colon during these procedures.
You will get written bowel prep instructions to follow at home before the procedure. The bowel prep cleans out the intestine so your doctor can see everything clearly. During a colonoscopy, you get medicines to keep you relaxed. You usually do not need them for a sigmoidoscopy.
NIH: National Institute of Diabetes and Digestive and Kidney Diseases
- Colorectal Cancer Screening Tests (American Cancer Society) Also in Spanish
- CT Colonography (Virtual Colonoscopy) (American College of Radiology, Radiological Society of North America) Also in Spanish
- Flexible Sigmoidoscopy (National Institute of Diabetes and Digestive and Kidney Diseases) Also in Spanish
- Understanding Bowel Preparation (American Society for Gastrointestinal Endoscopy)
Videos and Tutorials
- What to Expect from Your Colonoscopy Procedure (American Society for Gastrointestinal Endoscopy)
Statistics and Research
- Cancer Stat Facts: Colorectal Cancer (National Cancer Institute)
Journal Articles References and abstracts from MEDLINE/PubMed (National Library of Medicine)
- Article: Adenoma detection rate is not influenced by the time of day...
- Article: Low-residue versus clear liquid diet before colonoscopy: An updated meta-analysis of...
- Article: Smartphone education improves embarrassment, bowel preparation, and satisfaction with care in...
- Colonoscopy -- see more articles
Find an Expert
- ASGE: Find a Doctor (American Society for Gastrointestinal Endoscopy)
- National Institute of Diabetes and Digestive and Kidney Diseases