GOALS The goal is to find the risk of colorectal cancer after an episode of acute diverticulitis in conservatively treated patients. Secondly, to determine the benefit of colonoscopy in these patients. BACKGROUND In the Netherlands, it is a common practice to routinely perform a colonoscopy after an episode of conservatively treated diverticulitis to exclude a malignancy. Yet according to the Dutch guidelines, these patients should not undergo a colonoscopy on a routine basis. The aim of this study is to determine the benefit of a colonoscopy in patients who have been treated for diverticulitis conservatively. STUDY This retrospective study includes patients who were diagnosed with acute diverticulitis (Hinchey 0 and I) and were treated conservatively, with or without antibiotics. Only patients who underwent colonoscopy were included for analysis. In addition, the outcome (yes or no colorectal cancer) of colonoscopy was analyzed according to patients' presentation of alarm symptoms for colorectal cancer. RESULTS Between January 2008 and June 2013, 977 patients were treated conservatively for an episode of acute diverticulitis. Of those, 645 underwent colonoscopy during follow-up. Alarm symptoms for colorectal cancer were present in 205 patients. Nine of them were diagnosed with colorectal cancer (4.4%) versus 1 patient (0.2%, P=0.0002) in the group without alarm symptoms (N=440). CONCLUSIONS This study confirms that routine colonoscopy is not indicated after acute diverticulitis which has been treated conservatively in a large series. Only in case of alarm symptoms a colonoscopy is mandatory, but even then the actual finding of a colorectal cancer is rare.