Mechanical bowel preparation before elective colon resection has recently been questioned in the literature. We report a prospective study evaluating the anastomotic leak rate in patients undergoing elective colorectal surgery without preoperative mechanical bowel preparation. One hundred fifty-three patients undergoing elective colon resection from July 2006 to June 2008 were enrolled into this Institutional Review Board-approved study. All patients were operated on by a single surgeon at a single institution. No patients received mechanical bowel preparation. Of the 153 patients enrolled, 51.6 per cent had a colorectostomy, 32 per cent had an ileocolostomy, 10.4 per cent had a colocolostomy, 5.2 per cent had an ileoanal anastomosis, and 0.6 per cent had an ileorectostomy performed. A total of eight patients (5.2%) developed an anastomotic leak. Of these patients, four required reoperation, three were managed with percutaneous drainage, and one was managed with antibiotics alone. Five of the eight patients who developed an anastomotic leak had significant preoperative comorbidities, including neoadjuvant radiation therapy, diabetes mellitus, end-stage renal disease, prior anastomotic leak, and tobacco use. Elective colon resection can be performed safely without preoperative mechanical bowel preparation. Vigilance for anastomotic leak must be maintained at all times, especially in patients with comorbidities that predispose to anastomotic leak.