Objective: This study evaluates the effects of mechanical bowel preparation (MBP) on anastomosis below the peritoneal verge and questions the influence of MBP on anastomotic leakage in combination with a diverting ileostomy in lower colorectal surgery. Summary Background Data: In a previous large multicenter randomized controlled trial MBP has shown to have no influence on the incidence of anastomotic leakage in overall colorectal surgery. The role of MBP in lower colorectal surgery with or without a diverting ileostomy remains unclear. Methods: This study is a subgroup analysis of a prior multicenter (13 hospitals) randomized trial comparing clinical outcome of MBP versus no MBP. Primary end point was the occurrence of anastomotic leakage and secondary endpoints were septic complications and mortality. Results: Total of 449 Patients underwent a low anterior resection with a primary anastomosis below the peritoneal verge. The incidence of anastomotic leakage was 7.6% for patients who received MBP and 6.6% for patients who did not. Significant risk factors for anastomotic leakage were the American Society of Anesthesiologists-classification (P = 0.005) and male gender (P = 0.007). Of total, 48 patients received a diverting ileostomy during initial surgery; 27 patients received MBP and 21 patients did not. There were no significant differences regarding septic complications and mortality between both groups. Conclusion: MBP has no influence on the incidence of anastomotic leakage in low colorectal surgery. Furthermore, omitting MBP in combination with a diverting ileostomy has no influence oil the incidence of anastomotic leakage, septic complications, and mortality rate.