Background and study aims Diverticular disease or diverticulosis is a benign disease of the colon. Diverticulae are pockets of bowel wall which protrude through weaknesses in the muscular wall of the colon. The mechanisms leading to their formation remains unclear and is likely a complex interaction of multiple factors. For the majority of people these pockets are incidental findings they can become inflamed which is called diverticulitis. The main aim of this study is to see if a faecal samples, which will be tested for hidden blood content with a faecal immunochemical test for haemoglobin (FIT), could be used as an alternative to currently used follow-up investigations for patients who have an episode of acute diverticulitis confirmed on a computerised tomography (CT) scan. These are colonoscopy, sigmoidoscopy or a special CT called CT colonoscopy. The investigators will also be testing faecal calprotectin which is a marker of bowel inflammation and an assessment of the microbes that live in the bowel to see if this will provide further insights into the diagnosis and treatment of diverticulitis. Who can participate? All patients 18 or over admitted to a participating hospital with acute diverticulitis confirmed on a CT scan and who planned to have one of the currently used follow-up investigations are eligible. What does the study involve? The study will involve participants taking three stool (faecal) samples using faecal testing kits posted to participants. One is as close to their first solid stool after diagnosis as possible, the others are at 3 weeks after diagnosis and then 6 weeks after diagnosis. What are the possible benefits and risks of participating? There are no risks of participating. The investigators hope to demonstrate that a negative FIT test for patients after acute diverticulitis will be able to exclude a bowel cancer and prevent the majority of future patients having invasive and time consuming tests. There no additional benefit for participants for their current episode, as they will still need to have these tests. Where is the study run from? Royal Surrey County Hospital When is the study starting and how long is it expected to run for? 09/10/2023-30/09/2024 Who is funding the study? The study is being funded by MATTU (Minimal Access Therapy Training Unit), GUTS (GUTS - Fighting Bowel Cancer) and NHIR (National Institute for Health and Care Research). Who is the main contact? James Norman, On the study email rsch.colorectalDfitstudy@nhs.net