In elective colorectal surgery, the benefit of preoperative antibiotic prophylaxis is well established, with a reduction in wound infection rate to less than 10%. The antimicrobial agent used has to be active against aerobic and anaerobic pathogens such as Escheria coli and Bacteriodes fragilis. The efficacy of three schemes of administration: oral and/or parenteral prophylaxis associated with a mechanical preparation, has been demonstrated. Oral antibiotic administration is current practice in USA; the most widely used oral regimen is the combination of erythromycin and neomycin given the day before surgery. Parenteral prophylaxis with a cephalosporin active against Bacteriodes fragilis such as cefoxitin and cefotetan, is preferred in Europe. The issue of whether a systemic prophylaxis should be added to the oral regimen or not has not yet been resolved. However it seems that the association should be proposed in various situations: patients with a high risk factors score (rectal resection and operations lasting more than three hours), patients with incomplete mechanical preparation, delay of the onset of surgery after the last oral dose.