AimsWe aimed to investigate the association between the age at diagnosis of type 2 diabetes and the risk of cardiovascular (CVD) outcomes in comparison with nondiabetic counterparts. MethodsA total of 634,350 patients with newly diagnosed type 2 diabetes between January 1, 2012, and December 31, 2014 were included in a Korean population cohort study. Nondiabetic matched controls were selected from the general population in a 1:2 ratio. Participants were followed until the end of 2019 for CVD outcomes and mortality. ResultsDuring 5.7 years of follow-up, patients with type 2 diabetes diagnosed at ≤40 years of age had the highest excess risk for most outcomes relative to controls, with an adjusted hazard ratio (HR) (95 % CI) of 6.08 (5.51–6.70) for total mortality, 7.10 (6.66–7.58) for hospitalization for heart failure, and 5.04 (4.86–5.24) for coronary heart disease. All risks attenuated progressively with each increasing decade of diagnostic age. ConclusionIn this population-based cohort study, a younger age at diagnosis of type 2 diabetes was associated with a higher relative risk of mortality and CVD outcomes. Therefore, primary prevention of type 2 diabetes is desirable at all ages but is particularly important at younger ages.