Background: The aim was to evaluate the characteristics and cardiovascular complications of a large Belgian cohort of adults diagnosed with type 2 diabetes (T2DM) <45 years. Methods: Retrospective analysis of 886 patients diagnosed with T2DM <45 years and 933 T2DM patients diagnosed at the age between 60 and 70 years. To compare variables between groups, the independent t test or paired t test was used for normally distributed continuous variables, the Mann-Whitney's U-test for non-normally distributed continuous variables and the Chi squared test or McNemar test for categorical variables. Multivariable logistic regression was used to adjust for confounders. Results: In the young-onset T2DM cohort, the age at diagnosis was 37.3 +/- 6.4 years, 44.1% of patients were female and 12.1% were from an ethnic minority (EM) background. At last visit, age of patients was 57.3 +/- 12.5 years with a diabetes duration of 20.5 +/- 11.8 years and a mean HbA1c of 7.3% +/- 1.3 (56 mmol/mol +/- 14). Of all patients, 56.8% were obese, 49.9% were hypertensive, 34.1% did not reach the LDL cholesterol target and 20.1% had a cardiac event by time of last visit. Compared to women, men had a higher HbA1c [7.3% +/- 1.4 (56 mmol/mol +/- 15) vs. 7.1% +/- 1.2 (54 mmol/mol +/- 13), p = 0.021] and a significantly higher rate of cardiac events, even after adjustment for confounders (24.3 vs. 14.8%, p = 0.010). Compared to Caucasians, EM patients were younger at diagnosis (35.4 +/- 6.8 years vs. 37.6 +/- 6.2 years, p = 0.001) and were less often obese (43.3 vs. 55.6%, p = 0.007). Compared to the first visit, glycemic control improved [7.3% +/- 1.3 (56 mmol/mol +/- 14) vs. 7.9% +/- 1.7 (62 mmol/mol +/- 19), p < 0.0001] by the time of the last visit. Compared to the older-onset T2DM cohort, young-onset T2DM patients showed a higher HbA1c [7.3 +/- 1.3% (56 mmol/mol +/- 14) vs. 6.9 +/- 1.0% (51 mmol/mol +/- 11), p = < 0.0001] and a higher BMI (31.2 +/- 5.8 vs. 29.6 +/- 5.5 kg/ m2, p = < 0.0001) at last contact. When adjusted for age, diabetes duration, HbA1c and cardiovascular risk factors, there was no difference in cardiovascular events between the two cohorts. Conclusions: A diagnosis of T2DM <45 years has an important impact on patients' lives. Prevention measures are essential, but also specific attention to this high-risk group is needed for them to better achieve their therapeutic targets.