Colonoscopy is the standard method for detection and removal of colorectal adenomas, the precursor lesions of most colorectal cancers [1 -4]. Despite being the most sensitive method, colonoscopy does not fully protect a person from developing future colorectal cancer [5 -10]. This imperfection is for a major part caused by missed precancerous lesions due to inadequate bowel preparation, the presence of flat lesions that are difficult to detect [8,9,11], and the relative difficulty of visualizing lesions on the proximal side of haustral folds and the internal curves of flexures [12,13]. The latter may, at least partly, be caused by the fact that the use of standard 140°and 170°colonoscopes allows visualization of only approximately 90 % of the colonic surface [14]. Moreover, it has been shown that up to twothirds of missed lesions are located on the proximal side of folds [13]. The miss rates of colonoscopy have been widely acknowledged, with back-to-back colonoscopy studies showing polyp and adenoma miss rates of approximately 20 % -25 % in older studies [15] and up to 40 % in more recent studies evaluating novel technologies developed to improve visualization behind folds [16,17]. Alongside the implementation of quality indicators [1,18], technologies such as cap-assisted colonoscopy, virtual chromoendoscopy, Third Eye colonoscopy, and Full Spectrum Endoscopy (Fuse) colonoscopy have been developed to improve adenoma detection [16,17,19,20]. However, some of these techniques have been shown to increase only marginally the detection of adenomas, while others are less practical in use or demand high investments with a change in endoscopy platform [21,22]. Background and study aims: Adenoma miss rate during colonoscopy has become a widely acknowledged proxy measure for post-colonoscopy colorectal cancer. Among other reasons, this can happen because of inadequate visualization of the proximal aspects of colonic folds and flexures. EndoRings (EndoAid Ltd., Caesarea, Israel) is a silicone-rubber device that is fitted onto the distal end of the colonoscope. Its flexible circular rings engage and mechanically stretch colonic folds during withdrawal. The primary aim of this study was to compare adenoma miss rates between standard colonoscopy and colonoscopy using EndoRings. Methods: In this multicenter, randomized, tandem colonoscopy study, we performed same-day, back-to-back colonoscopies with EndoRings followed by standard colonoscopy, or vice versa. Results: After exclusion of 10 patients for protocol violations, 116 patients (38.8 % female; mean age 58.7) remained for analysis. The adenoma miss