Sigmoidoscopy is the visual examination of the inside of the rectum and sigmoid colon, using a lighted, flexible tube connected to an eyepiece or video screen for viewing. This device is called an endoscope. The colon (large intestine) is 5 to 6 feet long. During a sigmoidoscopy, only the last 1 to 2 feet of the colon is examined. This last part of the colon, just above the rectum, is called the sigmoid colon.