Patients undergoing elective surgery for left-sided colon resection are asked to participate in this study: Every patient undergoes two types of examinations (endoscopy, CT scan) on day 3, 4 or 5 postoperatively. These two procedures are subject to investigation in terms of their accuracy (sensitivity, specificity) in detection of anastomotic leaks. The patients are followed up until day 42 postoperatively. There are no other specific tests or examinations within the study. Information and informed consent are obtained preoperatively.