Background and aims: There is no current, evidence-based therapy to prevent acute diverticulitis in patients with diverticular disease. Metformin has been shown to have anti-inflammatory effects in a number of disease states, in both animal models and in human observational studies. The potential therapeutic efficacy of metformin in diverticular disease has not been investigated. This study aims to describe the relationship between metformin use and diverticular disease in patients with diabetes mellitus. Methods: This was a retrospective case–control study. It compared metformin and other hypoglycaemic medication use in diabetic patients with uncomplicated diverticulosis to those with acute diverticulitis. Patients were identified using hospital International Classification of Diseases 10 (ICD-10) data, and radiology, pathology and scanned medical record databases were used to confirm diagnoses and collect all information. Chi square tests were used to determine significance of difference in categorical variables, and Mann–Whitney tests were used for continuous data. Results: There were 174 patients with uncomplicated diverticulosis and 175 patients with acute diverticulitis. A diagnosis of acute diverticulitis was associated with a significantly lower incidence of metformin use, than a diagnosis of uncomplicated diverticular disease (44% compared to 60%, respectively, p =.002). Other oral hypoglycaemic drugs and insulin were not associated with a lower incidence of diverticulitis (p =.12 and p =.24, respectively). Conclusion: Metformin use is associated with reduced incidence of diverticulitis in diabetic patients with diverticular disease. The utility of metformin as a therapeutic agent to reduce the risk of diverticulitis in patients with diverticular disease warrants further randomised, prospective, interventional investigation.