The use of hematopoietic cell transplantation (HCT) for treating malignant conditions in children has increased over the past five decades, leading to a growing population of long-term survivors.This population of childhood HCT survivors faces increased risks of adverse medical effects due to cancer treatments, including adverse cardiovascular disease (CVD) risk factors such as metabolic syndrome, insulin resistance. but the impact of exposure to HCT preparative conditioning regimen has not been clearly delineated. These risk factors, including obesity, dyslipidemia, hypertension, and insulin resistance (IR), are significant contributors to premature cardiovascular disease and represent a leading cause of non-relapse deaths in childhood cancer and HCT survivors. This study aimed to assess the early development of CVD risk factors and their relationship to insulin resistance in a large population of pediatric and young adult HCT survivors of childhood hematologic malignancies. The study compared their cardiovascular risk profiles, insulin resistance (measured by euglycemic hyperinsulinemic clamp studies), and body composition (determined by dual X-ray absorptiometry - DXA) with a cohort of sibling controls. We enrolled 151 HCT recipients (26.36 ±0.90 years at study enrollment; time since HCT of 2.6-31.5 years) and 92 sibling controls to complete at cardiovascular risk assessment including insulin sensitivity by hyperinsulinemic euglycemic clamp, anthropometry, body composition by dual X-ray absorptiometry, blood pressure, and serum biomarkers. We used linear models to test for mean differences in all continuous outcomes between survivors and siblings, accounting for intra-family correlations with generalized estimating equations. Recipients of HCT were found to have lower insulin sensitivity and more likely to have adverse CVD risk factors in comparison to their healthy siblings. Significantly higher percent fat mass and visceral adipose tissue, and significantly lower lean body mass were noted in HCT recipients than sibling controls despite having a similar body mass index between the two groups. Total body irradiation in the conditioning regimen was one of the strongest factors associated with lower insulin sensitivity, dyslipidemia and abnormal body composition leading to sarcopenic obesity. This study reveals that pediatric and young adult HCT survivors are more insulin resistant and have a higher prevalence of adverse cardiovascular risk factors compared to sibling controls. The presence of cardiovascular risk factors at a relatively young age raises concerns about an escalating trajectory of cardiovascular disease in this population. Therefore, regular monitoring of HCT survivors for cardiometabolic risk factors and early intervention will be crucial for preventing cardiovascular-related complications in the future. The findings underscore the importance of survivorship care for pediatric and young adult HCT survivors, with a focus on managing cardiovascular risk factors and promoting a healthy lifestyle to mitigate long-term adverse effects. Early identification and targeted interventions can significantly improve the long-term health outcomes of this vulnerable population, reducing the burden of cardiovascular disease and related complications.