Adenoma detection rate (ADR) is a quality marker of colonoscopy and operator performance. Prior studies evaluating the effect of an extended workday on the ADR reported variable outcomes that remain controversial. Given the variable results of prior studies and the potential legal implications of reduced ADR in the afternoon, we aimed to further evaluate this parameter and its effect on ADR. We performed a systematic review of the PubMed, CINAHL and Scopus electronic databases. Studies were included if they reported ADR in patients undergoing colonoscopy in the morning session and the afternoon session. Afternoon sessions included both sessions following a morning shift and half-day block shifts. Subgroup analyses were performed for ADR comparing morning and afternoon colonoscopies in a continuous workday, advanced ADRs (AADRs) and polyp detection rates (PDRs) were also compared. Thirteen articles with 17 341 (61.2%) performed in the morning session and 10 994 (38.8%) performed in the afternoon session were included in this study. There was no statistical significance in the ADR or AADR between morning and afternoon sessions, respectively [relative risk (RR) 1.06, 95% confidence interval (CI) 0.99-1.14] and (RR 1.19, 95% CI 0.95-1.5). Afternoon procedures had a significantly higher PDR than morning procedures (RR 0.93, 95% CI 0.88-0.98). ADR was not significantly influenced in the afternoon session when operators continued to perform procedures throughout the day or on a half-day block schedule.