A flexible sigmoidoscopy is a procedure that a gastroenterologist will often perform in order to investigate the potential causes of abdominal pain, bleeding from the rectum or certain bowel changes. It is also performed as a preventive screening for colon and rectal cancer, typically in patients over 50 years old. Usually, no sedation is required for this procedure, during which the sigmoidoscope is directed through the rectum into the sigmoid colon and blows a small amount of air into the space so that the physician can better see the walls of the colon. The doctor then carefully examines the bowel lining as the sigmoidoscope is slowly withdrawn. While this procedure is very similar to a colonoscopy, it differs from it in that it does not require sedation, is less difficult to prep for and allows for examination of only part of the colon, as opposed to the entire colon. While both are effective means of screening for colon cancer, a colonoscopy is a more thorough exam that is recommended once every 10 years for patients over 50 while a sigmoidoscopy is recommended every five years.