Background: Colonoscopy is a gold standard tool for the screening of colorectal cancer. The effectiveness of colonoscopy is largely dependent on colonoscopist. Adenoma detection rate (ADR) is most widely used as an indicator of quality of operator’s skill. However, high ADR alone do not guarantee complete removal of polyps due to limitation of definition of ADR. For example, there is no difference in ADR, whether one or more polyps were removed in patients with multiple polyps. Therefore, other optimal indicator is needed to better reflect the quality of colonoscopist. In present study, we analyzed the association of several quality indicators such as the total adenoma detected per colonoscopy (APC), adenoma per positive participants (APP) and ADR-plus with adenoma missed rate (AMR). Method: Patients who underwent more than two total colonoscopy for screening, surveillance within 36 months in Korea University Ansan Hospital between January, 2011 and February 2016 were included. AMR and adenoma more than 5mm miss rate (AMR>5mm) were calculated from 5 endoscopists who performed total colonoscopy more than 40 times as a first colonoscopist and were in fellow training for more than 2 years. ADR, APC, APP and ADR plus were calculated from 100 colonoscopic results which were randomly selected from total colonoscopy performed by each colonoscopist. Results: A total of 238 patients aged≥40 years were analyzed retrospectively. Mean age was 59.6 years and male was 63.4%. And mean time interval between colonscopic exam was 18.4 months. There were no significant differences in age, sex, bowel preparation quality and mean time interval between colonoscopic exam among five endoscopists. ADR and other colonoscopic indicators were listed in table 1. AMR was 0.31, 0.44, 0.48, 0.35 and 0.27. AMR>5mm was 0.24, 0.23, 0.22, 0.39 and 0.17, respectively. AMR was negatively correlated with APC (r=-0.200, p=0.747), ADR plus (r=-0.100, p=0.873) and APP (r=-0.300, p=0.505), but these associations were not statistically significant. ADR was positively associated with AMR (r=0.600, p=0.285), but statistically insignificant. Whereas APC exhibited a strong inverse correlation with AMR>5mm (r=-0.900, p=0.037), the other indicators were not significantly correlated with AMR>5mm (r for ADR=-0.700, p=0.188; r for ADR plus =-0.800, p=0.104, r for APP =-0.300, p=0.624). Conclusion: APC had significant negative association with AMR>5mm. APC might be a better quality indicator for meticulous colonoscopist than ADR. The impact of APC on missed polyp and interval cancer needs to be investigated in a larger study.