Background/Aims: A dietary regimen consisting of a clear liquid diet (CLD) for at least 24 hours is recommended for colonoscopy preparation. However, this requirement results in problems in patient compliance with bowel preparation. The aim of this study was to evaluate the efficacy of a CLD compared with a regular diet (RD) for colonoscopy prepara-tion using a polyethylene glycol (PEG) solution. Methods: This was a multicenter, randomized, investigator-blind prospective study. A total of 801 healthy outpatients undergoing after-noon colonoscopy were randomized to either a CLD or RD in addition to a 4 L PEG regimen. Results: The quality of bowel cleansing was not different between the CLD and RD groups in terms of the proportion with excellent or good preparation. In addition, no significant differences were observed be-tween the two groups for polyp and adenoma detection rates and overall adverse events. Good compliance with bowel preparation was higher in the RD group than in the CLD group. Conclusions: A CLD for a full day prior to colonoscopy should not be mandatory for PEG-based bowel preparation. Dietary education concerning the avoidance of high-fiber foods for 3 days before colonoscopy is sufficient, at least for healthy outpatients. (Gut Liver 2013;7:681-687)