['Recent studies have shown the adenoma detection rate (ADR) to decrease from endoscopist fatigue.', 'Our primary objective was to evaluate the afternoon ADR in half-day versus full-day blocks. Secondary objectives were to determine whether time or complexity of prior procedures (modified queue position) influence ADR.', 'Retrospective chart review on consecutive colonoscopies.', 'Tertiary-care teaching hospital.', 'This study involved all patients in our database who were over age 45 and who underwent screening and surveillance colonoscopies.', 'ADR.', 'A total of 3085 patients were included in the study, with an overall 31% ADR. Of these procedures, 2148 (70%) were done in the morning, and 937 (30%) were done in the afternoon (512 full-day block, 425 half-day block). By multivariate analysis, there was no difference in ADR between full-day blocks compared with afternoon-only blocks (35% vs 32%; odds ratio [OR] 1.1; 95% confidence interval [CI], 0.8-1.5; P = .2). For all afternoon colonoscopies, no decrease in ADR was noted with increasing queue position (P = .9) or time (P = .3). In addition, no difference was found comparing ADR between all afternoon colonoscopies versus morning colonoscopies (33% vs 30%; OR 1.1; CI, 1.0-1.3; P = .1). No difference was found for advanced adenomas and number of adenomas between either afternoon-only blocks versus afternoon colonoscopy in full-day blocks or morning versus all afternoon cases.'] Is adenoma detection rate influenced by full-day blocks , time , or modified queue position?