On day 3, 4 or 5 postoperatively, all patients with colorectal resection and anastomosis will undergo a CT scan with intravenous (i.v.) and rectal contrast enema and a flexible endoscopy. Both are currently routine examinations. CT scan is performed before endoscopy because contrast enema clears the rectum and anastomotic area and no further cleaning measures are necessary. The timing of the CT scan and the endoscopy is chosen because early signs of anastomotic leak should be present and thus early therapeutic interventions before the development of peritonitis is possible. The standard treatment is not altered with the exception of the two described procedures. Due to infrastructural issues and weekends the CT scan and the endoscopy can be performed on either day (3,4,5 postoperatively).