Preoperative mechanical bowel preparation aims to rid the colon of solid stool, to reduce postoperative infectious complication rate. During the 20th century, this practice became a surgical dogma, and primary colonic anastomosis was considered unsafe in the face of unprepared bowel. More recently, several well-designed single-center randomized trials have suggested that bowel cleansing may have no benefit in reducing postoperative complication rate. None of these studies, however, had the statistical power to draw firm conclusions. Recently, two large multicenter studies with adequate power were published, showing no difference in the rate of anastomotic leak, wound infection, or other complications between patients who had preoperative mechanical bowel preparation, and those who had not. Despite this evidence, it seems that mechanical bowel preparation is still commonly practiced around the globe. A multicenter North American study is needed to change this time-honored surgical practice.