['Afternoon colonoscopies have recently been reported to be associated with lower adenoma detection rate (ADR), which was attributed to physician fatigue resulting from the same endoscopist performing procedures throughout the day. The aim of our study was to assess ADR in morning compared with afternoon colonoscopy performed in half-day blocks with different physicians. We evaluated the primary hypothesis that morning and afternoon ADRs would not differ significantly when performed in half-day blocks by different endoscopists.', 'Data on all colonoscopies performed between January 2009 and December 2009 were obtained from our endoscopy database. All patients who underwent colonoscopies in 2009 for screening, surveillance, and family history of colon cancer/polyps were included in the study. Morning colonoscopies were defined as those that were performed from 0800 to 1200 hours. Afternoon colonoscopies were defined as those that were performed from 1300 to 1700 hours. Colonoscopies in each block were performed either by different endoscopists working in half-day (morning or afternoon) block schedules or by the same endoscopist working a full-day schedule.', 'A total of 4,665 patients were included in the study. For endoscopists working the full-day, the afternoon ADR was significantly lower than the morning ADR (21 vs. 26.1%; odds ratio (OR)=0.75; 95% confidence interval (CI) 0.59, 0.96; P=0.02). Conversely, in the half-day group, there was no significant difference in ADR between afternoon and morning (27.6 vs. 26.6%; OR=1.05; 95% CI 0.88, 1.26; P=0.56).'] Is adenoma detection rate influenced by the timing of colonoscopy when performed in half-day blocks?