Subjects who underwent colonoscopy for various reasons were included. After agreeing to participate in the study, study participants were randomly assigned to split dose or same day dose group. Bowel cleansing is done using polyethylene glycol (PEG). All colonoscopy was done between 10 AM to 6 PM. Study participants were instructed to ingest 500ml PEG every 15 minutes. Subjects who were assigned to split dose group ingested 2L PEG from 9PM 1 day before colonoscopy. Remaining 2L PEG was ingested 3-5 hours before colonoscopy. In the same-day dose group, bowel cleansing was started from 5AM for subjects who were scheduled to receive colonoscopy in the morning. Afternoon colonoscopy group in the same-day dose group ingested 2L PEG from 5AM. Remaining 2L PEG was finished 3-5 hours before colonoscopy.