The purpose of this study is to describe our experience with cases of false negative findings at conventional colonoscopy (CC) that were identified by CT colonography (CTC). Conventional colonoscopy (CC) is the universally accepted gold-standard technique for the diagnosis of colonic polyps and cancers, however occasionally this method can generate false negative findings. We present examples of false negatives at CC, correctly identified by CT colonography (CTC), and later confirmed at a second endoscopy, describing the reasons of false negative, when possible.CT colonography is a highly sensitive technique for polyps and colorectal cancer (CRC) detection [1] across a broad spectrum of accepted indications and protocols (preparation, fecal tagging, CO 2 automatic insufflation, hypotonization). Its sensitivity is high especially for detecting polyps greater than 10 mm; however, CTC is less accurate than CC for small and diminutive polyps [1][2][3][4].However, when CC is performed by inexperienced operators and non-gastroenterologists or when lesions have atypical morphologies disappointing low sensitivities may occasionally be reported [5]. The commonalities of typical lesions missed at CC usually concern their location and shape: false negative results can be generated when incomplete colonoscopies are performed (cecum not reached), when lesions are hidden behind haustral folds or when they are flat or present atypical morphologies. On the other side, typical lesions missed at CTC are usually located in the rectosigmoid colon and in the splenic flexure, due to a minor effect of the insufflation in this segments [1]. Right colon is usually easier to distend and consequently evaluate at CTC, while the increased distance in CC makes right colon assessment more difficult. For the above reported reasons CT colonography and CC should be considered equivalent in terms of sensitivity in CRC detection and complementary [1].