AbstractBackgroundPrevious research shows that obesity, unhealthy eating, physical inactivity and a high use of psychotropic medications are prevalent among persons with intellectual disability (ID), which might increase the risk of type 2‐diabetes (T2DM). This study aims to investigate: (1) whether persons with ID have an increased risk of T2DM compared with an age‐ and sex‐matched reference group and (2) differences in T2DM risk by sex, birth year, ID inclusion diagnosis and ID severity.MethodsThis study is a nationwide cohort study, including 65 293 persons with ID and 659 723 persons in an age‐ and sex‐matched reference group without ID. Incidence rates for T2DM were calculated and Cox proportional regression models were used to estimate adjusted hazard ratios (aHRs) for the association between ID and T2DM. Follow‐up began from the 1 January 1977 (when T2DM data were available), participants' 22nd birthday or from the date the participants immigrated to Denmark, whichever came last and continued until the onset of T2DM, emigration, death or end of follow‐up (31 December 2021), whichever came first.ResultsPersons with ID had more than double risk of T2DM compared with the reference group [aHR = 2.15, 95% confidence interval (CI): 2.09–2.20]. The strongest associations were found among women, persons born between 1980 and 1999 and among persons with mild ID.ConclusionsPersons with ID have an increased risk of T2DM. This knowledge is important in relation to the development and prioritising of preventive initiatives among persons with ID in the healthcare sector. Future research should focus on the underlying mechanisms that can explain the possible association between ID and T2DM as it allows a more targeted prevention strategy.