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
- Colonoscopy: When You Need It -- and When You Don't (ABIM Foundation)
- Your Doctor Has Ordered a Colonoscopy: What Questions Should You Ask? (American College of Gastroenterology) - PDF
- 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
- Frequently Asked Questions about Colonoscopy and Sigmoidoscopy (American Cancer Society)
- Understanding Bowel Preparation (American Society for Gastrointestinal Endoscopy)
- Virtual Colonoscopy (National Cancer Institute)
Statistics and Research
- CDC Vital Signs: Colorectal Cancer (Centers for Disease Control and Prevention)
- CDC Vital Signs: Colorectal Cancer Tests Save Lives (Centers for Disease Control and Prevention) Also in Spanish
Journal Articles References and abstracts from MEDLINE/PubMed (National Library of Medicine)
Find an Expert
- ASGE: Find a Doctor (American Society for Gastrointestinal Endoscopy)
- National Institute of Diabetes and Digestive and Kidney Diseases