['The miss rate of colon polyps and its related factors have not been clearly identified yet. This study aims to review the miss rate of polyps both on the patient-level and on the polyp-level and to analyze the factors affecting the miss rate such as those related to the endoscopist, procedure, patient, and polyp.', 'From August 2011 to August 2013, patients who underwent elective second colonoscopy for resection of polyps, the sizes of which were not small enough to be resected by biopsy forceps alone at first colonoscopy, were enrolled retrospectively.', 'The miss rate on the patient-level was 59.2% (234/395) and on the polyp-level was 27.9% (578/2,068). There was no significant difference in the miss rate depending on the experience of the endoscopists or characteristics of the patients. In terms of the procedure, the miss rate was higher when the colonoscopy was performed in the afternoon (OR 1.632, p=0.046). It was found that the miss rate of polyps increased when the polyps were small (OR 4.595, p<0.001 in <5 mm/OR 3.447, p<0.001 in 5-10 mm), flat or sessile (OR 2.406, p<0.001 in flat/OR 1.768, p=0.002 in sessile), and located in the left colon (OR 1.391, p=0.007).'] Do [ Factors influencing the miss rate of polyps in a tandem colonoscopy study ]?