en Internal Internal Original Article Original Article Background: The appropriate colon cleansing is a major determinant of quality of colonoscopy. The aim of this study was to compare the efficacy and tolerability of the morning (AM) PEG (polyethylene glycol) solution to previous-evening (PM) PEG solution for the afternoon colonoscopy. Methods: This comparative study compared the AM to PM prep for afternoon outpatient colonoscopy. The subjects randomly received PEG PM dose 4 liters of water plus 4 pack PEG powder at 6 pm before colonoscopy (250 ml every 15 min) or AM ( the same dose solution at 6 am on the day of colonoscopy). The preparation and colonoscopy quality, PEG side effects, sleep quality, lesion detection, flush need and suction fluid were compared in these two groups. Results: One hundred seven cases received AM prep and 102 received PM prep. The colon prep was adequate in 94.4% in AM group and in 90.2% cases in PM group (P=0.2). The incidence of adverse events in these two groups was similar. Sleep quality and the need for flush was lower in the AM group (P=0.004 and P=0.03). The mean volume of suction fluid was higher in the AM group (P=0.01). The detected lesions were similar between the two groups. Adequate prep was associated with lower flush need in AM group (P=0.001). Conclusion: AM and PM PEG solutions were clinically equivalent with cleansing efficacy and side effect and lesion detection. AM group was associated with a better sleep quality and less flush need, but more suction fluid. Colonoscopy, Colon, cleansing, PEG solution, PM, AM 162 166 http://caspjim.com/browse.php?a_code=A-10-62-188&slc_lang=en&sid=1 Kobra Baghbani 10031947532846001727 10031947532846001727 No Babol University of Medical Sciences Javad Shokry-Shirvani javadshory@gmail.com 10031947532846001728 10031947532846001728 Yes Babol University of Medical Sciences Hassan Taheri 10031947532846001729 10031947532846001729 No Babol University of Medical Sciences