International guidelines recommend colonoscopy following hospitalisation for acute diverticulitis. There is a paucity of evidence supporting the efficacy of colonoscopy in this context, particularly for patients with CT-diagnosed uncomplicated left-sided diverticulitis. This study aims to investigate the frequency that colorectal cancer (CRC) and advanced adenomas (AA) are identified during follow-up colonoscopy after hospitalisation with CT-proven left-sided diverticulitis for the first time in a UK population. In this single-centre retrospective-cohort study all patients presenting with CT-diagnosed uncomplicated left-sided diverticulitis between 2014 and 2017 were identified. The incidence of histologically confirmed CRC and AA identified at follow-up colonoscopy 4–6 weeks following discharge was assessed. 204 patients with CT proven uncomplicated left-sided diverticulitis underwent follow-up colonoscopy. 72% were female and the median age was 63 years. There were no major complications. 22% of patients were found to have incidental hyperplastic polyps or adenomas with low-grade dysplasia. No CRC or AA were found. Routine colonoscopy following acute diverticulitis in this cohort did not identify a single CRC or AA and could arguably have been omitted. This would significantly reduce cost and pressure on endoscopy departments, in addition to the pain and discomfort that is commonly associated with colonoscopy.