We found no controlled studies published since Song and Glennys systematic review.5 The conclusions of the review about the efficacy of antibiotic prophylaxis therefore remain unchanged. The four studies included in the review1-4 consistently found that pre- and peri-operative antibiotics substantially reduced the risk of post-operative infection. The results support the reviews conclusions that antibiotic prophylaxis is effective in colorectal surgery and that the size of the reduction is clinically important. This conclusion is likely to apply to patients undergoing elective or emergency colorectal surgery, many of whom have malignant disease. The strength of the evidence for this conclusion is only moderate because of important methodological flaws within the trials reviewed. It is, however, unlikely that further trials will be carried out to provide stronger evidence. Further research is likely to focus on the cost-effectiveness of different antibiotic regimens and to help to shape policies to discourage inappropriate antibiotic use, including the provision of prophylaxis for longer than necessary.