A sigmoidoscopy is an internal examination of the lower part of the large intestine (colon), the inside of the rectum and the sigmoid colon—about the last two feet of the large intestine. A small biopsy instrument to remove tissue samples to be checked under a microscope for signs of disease can be performed during the examination.
A colonoscopy is a visual examination of the entire large intestine, also known as the colon. This examination is used to explore possible causes of abdominal pain, rectal bleeding, chronic constipation, chronic diarrhea and other intestinal problems. A colonoscopy is also used as a method of screening for colon cancer.