Bowel preparation has been a much-debated issue for both colonoscopy and for colorectal surgery. While bowel preparation for colonoscopy is clearly mandatory for optimal intraluminal visualization, bowel preparation for surgery has recently been challenged. This review evaluates oral bowel preparation, based on evidence in the literature, in order to provide a practical guide for physicians and practitioners about oral bowel cleansing preparations in current use for both colonoscopy and for colorectal surgery.A MEDLINE search, limited to publications in English language, was done through Ovid including articles published from 1966 to 2007 about bowel preparation using terms 'pre-operative care' and 'colonoscopy' or 'surgical procedure' associated with 'polyethylene glycol' and 'sodium phosphate'. The references lists from the identified articles were also included in the review. No bowel preparation method meets the ideal criteria for bowel cleansing prior to colonoscopy. However, polyethylene glycol-electrolyte lavage solution (PEG-ELS) and sodium phosphate are the most commonly used bowel preparations before colonoscopy and colon surgery. Both preparations are safely used and effective; however, some precautions should be considered, particularly with sodium phosphate. In addition, the efficacy of low-volume PEG-ELS can be improved by the addition of preparation adjuncts. Timing and dose are important considerations regardless of the method used. Mechanical bowel preparation for surgery has been questioned, and shown to have no extra benefits and possibly the association with increased morbidity. Regardless of the evidence, there are many randomized controlled trials showing the lack of benefit of mechanical bowel preparation.