Virtual colonoscopy is a non invasive technique allowing to study the colon from the inside, as conventional colonoscopy, without introducing an endoscope. Virtual colonoscopy is able to study the entire colon and its pathologies, allowing an early detection of its pathology without risks or contraindication. Virtual colonoscopy is an accurate, risk free and well tolerated technique now officially considered a valid option in colorectal cancer screening. Nowadays the well recognized indication of CT colonography examination are: for the prevention of colon-rectum cancer (screening), for all the individuals at average risk, men and women over 50 years old, as reported by colorectal cancer screening guidelines, published in march 2008 by the American Cancer Society. For diagnosis: for all the patients with intestinal disorder for whom a radiological or endoscopical study of the colon is required, to complete a conventional endoscopy in those patients where conventional examination is incomplete for several reason; and in those elderly patients with some contraindication for conventional examination.