Adenoma detection rate (ADR) is the primary quality indicator in screening colonoscopy. Apart from the withdrawal time and the quality of bowel preparation, the experience of colonoscopist can affect ADR. ADR >25% is recommended as the minimum level for good practice in colonoscopy. The limited experience of trainee may result to low ADR.Therefore, it is important for many training institutions to overcome this limitation by having colonoscopies of trainees performed under the supervision of experienced attending staff. In addition, the number of adenomas per total exams can reflect the vigilance of the colonoscopist because the “one and done colonoscopist” may achieve the standard ADR level while having a low number of detected adenomas per total exams.