Objectives To investigate the association between type 2 diabetes and risk of diverticular disease. Unlike previous studies, which have found conflicting results, we aimed to distinguish between diabetes types and adjust for modifiable risk factors. Design Observational cohort study. Setting Population-based Danish medical databases, covering the period 2005-2018. Participants Respondents of the 2010 or the 2013 Danish National Health Survey, of which there were 15 047 patients with type 2 diabetes and 210 606 patients without diabetes. Primary and secondary outcome measures Hazard ratios (HRs) for incident hospital diagnosis of diverticular disease adjusted for survey year, sex, age, body mass index (BMI), physical activity intensity, smoking behaviour, diet and education based on Cox regression analysis. As latency may affect the association between type 2 diabetes and diverticular disease, patients with type 2 diabetes were stratified into those with <2.5, 2.5-4.9 and ≥5 years duration of diabetes prior to cohort entry. Results For patients with and without diabetes the incidence rates of diverticular disease were 0.76 and 0.54 events per 1000 person years, corresponding to a crude HR of 1.08 (95% CI 1.00 to 1.16) and an adjusted HR of 0.88 (95% CI 0.80 to 0.96). The HR was lower among patients with ≥5 years duration of diabetes (adjusted HR: 0.76, 95% CI 0.67 to 0.87) than among those with 2.5-4.9 years or <2.5 years duration. Conclusion We found that patients with type 2 diabetes had a higher incidence rate of diverticular disease compared with patients without diabetes. However, after adjustment for modifiable risk factors, driven by BMI, type 2 diabetes appeared to be associated with a slightly lower risk of diverticular disease. Lack of adjustment for BMI may partially explain the conflicting findings of previous studies.