Background: Preoperative bowel preparation is still routinely used prior to colorectal surgery. This concept is based on traditional and personal empiricism and usually not evidence based. The objective of the present review was to reassess this dogma against the background of the highest level of evidence published thus far. Methods: The Medline database was searched using the search terms 'preoperative', 'bowel' and 'preparation' limited to 'randomized controlled trials' and 'meta-analyses'. Ten randomised controlled trials and seven meta-analyses comparing orthograde bowel cleansing to no preoperative bowel preparation were considered for rates of anastomotic leakages, surgical infections and other types of complications, reoperations and mortality. Results: All the most recent meta-analyses showed a significant increase of anastomotic dehiscences in patients with preoperative orthograde bowel cleansing. Additionally, a trend towards higher rates of surgical infectious complications and re-operations was revealed. Mortality remained unchanged by preoperative orthograde bowel cleansing. Conclusion: Routine preoperative orthograde bowel cleansing is no longer justified prior to colorectal surgery in general due to increased risk of anastomotic leakages. Further investigations should focus on different types of bowel preparation in situations where preoperative bowel preparation still may have a role such as total mesorectal resection with low anastomosis and protective ileostomy.