BACKGROUND Colonoscopy reduces colorectal cancer mortality and morbidity principally by the detection and removal of colon polyps. It is important to retrieve resected polyps to be able to ascertain their histologic characteristics. OBJECTIVE The aim of the study was to evaluate the cause of polyp retrieval failure. METHODS Bowel cancer screening colonoscopy data were collected prospectively. METHODS The Bowel Cancer Screening Program in the National Health Service. METHODS Screening participants were referred to our screening center after a positive fecal occult blood test result. METHODS A total of 4383 polyps were endoscopically removed from 1495 patients from October 2006 to February 2011. METHODS The number, size, shape, and location of polyps; polyp removal method; quality of bowel preparation; total examination time; and insertion and withdrawal times in collected data were examined retrospectively. RESULTS The polyp retrieval rate was 93.9%, and the failure rate was 6.1%, thus 267 polyps were not retrieved. In univariate analysis, factors affecting polyp retrieval failure were small polyp size, sessile polyps, and cold snare polypectomy (P < .001). Polyp retrieval was less successful in the proximal colon (P = .002). In multivariate analysis, polyp size and method of removal were independent risk factors for polyp retrieval failure (P < .001). CONCLUSIONS Retrospective study. CONCLUSIONS Small polyp size and cold snare removal were found to be significantly associated with polyp retrieval failure. It was difficult to retrieve small, sessile, and proximal colon polyps. Optical diagnosis could be an efficacious option as a surrogate for histologic diagnosis for these lesions in the near future.