Background:A recent meta-analysis has questioned the value of bowel preparation in patients undergoing colorectal resection. The aim of this clinical trial was to evaluate whether a single phosphate enema was as effective as oral polyethylene glycol (PEG) solution in preventing anastomotic leakage.Methods:Patients were randomized to receive either a single phosphate enema or 3 litres of oral PEG solution before surgery. Patients were followed for a minimum of 6 weeks to detect anastomotic leakage.Results:There were 147 patients in each group and the groups were evenly matched for putative risk factors at baseline. Patients in the enema group had more anastomotic leaks requiring reoperation than those in the PEG group (4·1 versus 0 per cent, P = 0·013; relative risk 2·04 (95 per cent confidence interval (c.i.) 1·82 to 2·30)). The mortality rate was higher in the PEG group (2·7 versus 0·7 per cent, P = 0·176; odds ratio 1·62 (95 per cent c.i. 0·45 to 36·98)).Conclusion:Bowel preparation with a phosphate enema was associated with an increased risk of anastomotic leakage requiring reoperation compared with oral PEG. These results do not support the routine use of a phosphate enema in patients undergoing elective colorectal surgery. Copyright © 2006 British Journal of Surgery Society Ltd. Published by John Wiley & Sons, Ltd.