A good bowel preparation regime is one that is not only effective in cleansing the colon but should be relatively small in volume and well-tolerated by patients with minimal adverse gastrointestinal symptoms. At our centre, reduced-volume 2-litre PEG-ELS plus bisacodyl and low fiber diet is used for bowel preparation for patients undergoing colonoscopy. Patients undergoing morning outpatient colonoscopy would normally ingest the PEG-ELS and bisacodyl the day before. This regime has been shown to be better tolerated by patients without compromising the quality of bowel preparation when compared with conventional 4-liter PEG-ELS. However, previous study on patient satisfaction found that nearly half of the patients attending the outpatient colonoscopy service at our centre were dissatisfied with the bowel preparation regime used. Of the seven items considered in the evaluation of patient satisfaction, comfort level during bowel preparation was the main cause of unfavorable responses. Moreover, a separate study using the same bowel preparation regime at our centre found a high percentage of poor quality bowel preparation, which was associated with increased technical difficulty and patient discomfort during colonoscopy. There was clearly a need for a better bowel preparation regime. Current literature suggests that either taking reduced-volume PEG-ELS on the same morning instead of the previous evening, or splitting the bowel preparation, would be better. However, whether the former or the latter is better, is unknown. The aim of our study was to compare the use of same-morning whole-dose reduced-volume PEG-ELS and split-dose reduced-volume PEG-ELS for bowel preparation for patients undergoing morning outpatient colonoscopy.