Scarce evidence is available for prognosis in adult-onset type 1 diabetes (T1D). The aim of this study is to investigate the risk of all-cause mortality, cause-specific mortality, and incident CVD in adult-onset T1D, as compared to type 2 diabetes with comparable age at diagnosis and population controls. We will explore potential modifiable factors including lifestyle and clinical characteristics that contribute to T1D prognosis. In addition, we will estimate the life expectancy associated with different age at T1D diagnosis as compared to population controls. This study will be based on people with diabetes recorded in Swedish National Diabetes Registers, with linkages to other nationwide registers to retrieve data on lifestyle factors, biomarkers, treatment and outcome information.