Objective: This study aimed to investigate premature mortality and the risk of cardiovascular disease (CVD) in Chinese adults with diabetes diagnosed before the age of 45 years. Methods A total of 519 participants with normal glucose tolerance (NGT) and 630 with newly diagnosed diabetes mellitus (DM) were recruited in 1986 in the Da Qing Diabetes Study. In 2009, the participants were followed up to assess mortality and CVD events. The subjects were stratified into four subgroups according to age and diabetes status: age <45 years with NGT (NGT(<45y)), age <45 years with DM (DM<45y), age >= 45 years with NGT (NGT(>= 45y)), and age >= 45 years with DM (DM >= 45y). The risk of death and CVD events in patients with young-onset DM and elder subjects with NGT were compared to show the extent of premature death and CVD in the DM participants. Results During the 23-year follow-up, 26 (10.40%) participants in NGT(<45y), 72 (34.12%) in DM<45y, 74 (30.58%) in NGT(>= 45y), and 266 (68.73%) in DM >= 45y died, including 13 (5.20%), 36 (17.06%), 24 (9.92%), and 128 (33.07%) death attributed to CVD. The corresponding rates of CVD events were 56 (22.40%), 90 (42.65%), 89 (36.78), and 213 (55.04%). It also showed that the risk of all-cause death (HR 1.23, 95% CI 0.88-1.71) or CVD events (HR 1.25, 95% CI 0.93-1.69) did not differ significantly between the DM<45y and NGT(>= 45y) groups after adjusting for sex, smoking, body mass index, systolic blood pressure, total cholesterol and previous history of CVD. Of note, participants in the DM<45y group had an higher risk of CVD mortality compared with that in the NGT(>= 45y) group (HR 1.76, 95% CI 1.04-2.98), although the mean age in the former group was 12 years lesser than that in the latter group (39.015.00 vs 51.45 +/- 5.14). Conclusions Young-onset diabetes is a risk factor for the premature death and cardiovascular disease. Early prevention and intensive treatment are warrented in patients with young-onset diabetes.