BACKGROUND: Variations in colonoscopy practice exist, which may be related to healthcare quality. AIMS: To determine factors associated with three performance indicators of colonoscopy: complete colonoscopy, adenomatous polyp diagnosis, and duration. PATIENTS: Consecutive patients referred for colonoscopy from 21 centres in 11 countries. METHODS: This prospective observational study used multiple variable regression analyses to identify determinants of the quality indicators. RESULTS: Six thousand and four patients were included in the study. Patients from private, open-access centres (odds ratio: 3.17, 95% confidence interval: 1.87-5.38) were more likely to have a complete colonoscopy than patients from public, gatekeeper centres. Patients from centres where over 50% of the endoscopists were of senior rank were roughly twice as likely to have an adenoma diagnosed, and longer average withdrawal duration (odds ratio: 1.08, 95% confidence interval: 1.07-1.09) was associated with more frequent adenoma diagnoses. Patients who had difficulty during colonoscopy had longer durations to caecum (time ratio: 2.87, 95% confidence interval: 2.72-3.01) and withdrawal durations (time ratio: 1.26, 95% confidence interval: 1.18-1.33) than patients who had no difficulties. CONCLUSIONS: Multiple factors have been identified as being associated with key quality indicators. The non-modifiable factors permit the identification of patients who may be at greater risk of not having quality colonoscopy, while changes to the modifiable factors may help improve the quality of colonoscopy.