BACKGROUND: The Global Rating Scale (GRS) comprehensively evaluates the quality of an endoscopy department, providing a patient-centred framework for service improvement.OBJECTIVE: To assess patient experiences during colonoscopy and identify areas that need service improvement using the GRS.METHODS: Consecutive outpatients undergoing colonoscopy were asked to complete a pre- and postprocedure questionnaire. Questions were based on GRS items and a literature review. The preprocedure questionnaire addressed items such as patient characteristics and information provision. The postprocedure questionnaire contained questions regarding comfort, sedation, the attitude of endoscopy staff and aftercare.RESULTS: The preprocedure questionnaire was completed by 1187 patients, whereas the postprocedure part of the questionnaire was completed by 851 patients (71.9%). Fifty-four per cent of patients were first seen in the outpatient clinic. The indication for colonoscopy was explained to 85% of the patients. Sixty-five per cent of the patients stated that information about the risks of colonoscopy was provided. Sedation was used in 94% of the patients; however, 23% judged the colonoscopy to be more uncomfortable than expected. Ten per cent of patients rated the colonoscopy as (very) uncomfortable. Preliminary results of the colonoscopy were discussed with 87% of patients after the procedure. Twenty-one per cent of the patients left the hospital without knowing how to obtain their final results. Being comfortable while waiting for the procedure (OR 9.93) and a less uncomfortable procedure than expected (OR 2.99) were important determinants of the willingness to return for colonoscopy.CONCLUSIONS: The present study provided evidence supporting the GRS in identifyng service gaps in the quality of patient experiences for colonoscopy in a North American setting. Assessing experiences is useful in identifying areas that need improvement such as the provision of pre- and postprocedure information.