Background <p>The relationship between obesity and cardiovascular disease (CVD) in obese patients with young-onset diabetes remains unclear. We investigated the incidence of CVD and the impact of changes in abdominal obesity status over time among patients with young-onset diabetes.</p> Methods <p>We defined young-onset diabetes as diagnosed before the age of 40. We analyzed data from 93,453 adults aged 20–39 with diabetes who underwent health screening between 2009 and 2011 and were followed up until 2021, using a customized Korean National Health Insurance Service database. Participants were categorized into four groups according to changes in abdominal obesity status: non-obese/non-obese, non-obese/abdominal obesity, abdominal obesity/non-obese, and persistent abdominal obesity. Hazard ratios (HRs) of the risk of CVD were calculated using Cox’s proportional hazards model, adjusting for age, gender, smoking status, alcohol consumption, physical activity, and use of antihypertensives and lipid-lowering therapies.</p> Results <p>HR for all CVD events was 1.53 (95% CI, 1.42–1.65) in those with abdominal obesity compared to non-obese individuals based on the baseline abdominal obesity status. The group with persistent abdominal obesity during the follow-up period had a higher incidence of all CVD (HR, 1.59; 95% CI, 1.42–1.77), coronary heart disease (HR, 1.56; 95% CI, 1.35–1.80), stroke (HR, 1.57; 95% CI, 1.28–1.91), and heart failure (HR, 1.69; 95% CI, 1.29–2.22) compared to the non-obese group. In participants who transitioned from abdominal obesity to a non-obese status, the incidence of hemorrhagic stroke (HR, 1.40; 95% CI, 0.80–2.44) and heart failure (HR, 0.98; 95% CI, 0.62–1.55) was not significantly higher than the group maintaining a non-obese state.</p> Conclusions <p>Abdominal obesity in young adults with diabetes is associated with a higher risk of CVD. Reducing waist circumference may mitigate the risk of hemorrhagic stroke and heart failure in this population.</p>