The purpose of the study was to examine whether a higher aerobic fitness in 9-10 year old children is related to superior macro and microvascular health and cardiovascular disease (CVD) risk. Ninety-six 9-10 year olds (53 boys) completed the study. Body composition was assessed from air displacement plethysmography and magnetic resonance imaging. Peak oxygen uptake (V̇O₂) was assessed from a ramp-incremental cycling exercise test. Macrovascular outcomes were assessed from pulse wave analysis and pulse wave velocity (PWV) using applanation tonometry. Microvascular function was assessed from the functional microvascular reserve and skin erythrocyte flux after iontophoretic application of skin vasodilators. Assessment of CVD risk was assessed via body mass index, total body fat percentage and visceral adipose tissue, glucose, triglyceride, total cholesterol, HDL cholesterol and LDL cholesterol, while insulin resistance was calculated using Homeostatic model assessment. Aerobic fitness groups (higher vs lower) were calculated from V̇O₂ peak scaled for body mass (mL·kg^-0.61·min^-1) and fat free mass (mL·FFM^-1·min^-1). Children with a higher V̇O₂ peak scaled for body mass had a greater carotid to ankle PWV compared to those with lower aerobic fitness (mean ± SD: 6.08 ± 0.47 vs. 5.87 ± 0.43 m·s^-1; p = 0.039), although this became non-significant when scaled for FFM (p = 0.56). No other mean differences in vascular or CVD risk health markers were present between higher and lower groups of aerobic fitness when scaled for body mass or FFM. Conclusion: Directly assessed aerobic fitness is not related to macro and microvascular health outcomes or CVD risk markers in 9-10 year olds.

• Children with a greater aerobic fitness had a higher carotid to ankle PWV compared to the lower fitness group when scaled for body mass, but not when adjusted for FFM.

• When split into higher and lower groups for aerobic fitness and adjusted for TBF%, no differences in CVD risk factors were observed.

• Higher levels of aerobic fitness, irrespective of normalisation for body mass or FFM, was not associated with improved vascular or CVD risk health outcomes in 9-10 year old children.