BACKGROUND/AIMS: Attempts to increase colonoscopy withdrawal time have been the topic of several recent publications. We assessed whether the real-time measurement of withdrawal time affected the withdrawal time and polyp detection rate. METHODS: Real-time colonoscopy withdrawal time was measured in 197 subjects in a study group and 184 subjects comprised a control group without real-time measurements. Colonoscopies were performed by four endoscopy specialists and three fellows during their first year of training. Withdrawal time, clinical features, bowel preparation, and polyp detection rates were comparatively analyzed. RESULTS: No significant differences in age, gender, bowel preparation, or polyp history were found in the two groups. Withdrawal time was significantly higher in the study group than that in the control group when a fellow performed the withdrawal. However, polyp detection rate did not significantly increase in the study group, regardless of physician. CONCLUSIONS: Real-time measurement of colonoscopy withdrawal time did not increase polyp detection rate, but the withdrawal time was significantly higher when a fellow performed the withdrawal phase than when a specialist performed withdrawal. Therefore, the real-time measurement of colonoscopy withdrawal time seems to be a useful tool for fellow training.