Background: Adverse Childhood Experiences (ACEs) are stressful events in early life (neglect, parental substance abuse, household mental illness, etc.) that are associated with an increased lifetime risk for chronic diseases, including cardiovascular disease (CVD). It is estimated that 64% of US adults have at least one ACE and 17% have four or more ACEs. Endothelial dysfunction is a key early marker of cardiovascular disease and may provide insight into subclinical vascular changes. This study aimed to investigate whether exposure to ACE’s is associated with impaired endothelial function in young, apparently healthy adults. Methods: Twenty-nine young adults (ages 18–29), apparently healthy, were stratified into high (>4 ACEs; n=14) and low (≤4 ACEs; n=15) ACE exposure based on the self-reported standardized ACE questionnaire. Endothelial function was assessed using brachial artery flow-mediated dilation (FMD), a validated, noninvasive ultrasound technique that measures vascular response at rest, occlusion, and post-occlusion. Additional physiological measures were collected, including body mass index (BMI), systolic and diastolic blood pressure, heart rate, C-reactive protein (CRP), and hemoglobin A1c (HbA1c). Group comparisons were performed using independent t-tests, with p < 0.05 considered statistically significant. Results: Participants who reported a high number of ACEs presented with significantly lower FMD compared to those who experienced lower numbers of ACEs (> 4 ACEs: 6.7 ± 4.0% vs. ≤4 ACEs: 10.6 ± 5.0 %; p = 0.041), indicating reduced endothelial function. When normalized to shear rate, FMD remained significantly lower in the high ACE group (> 4 ACEs: 0.2 ± 0.1 vs. ≤4 ACEs: 0.4 ± 0.3; p = 0.030). Baseline artery diameter (p = 0.242), peak diameter (p = 0.503), and diameter during occlusion (p = 0.277) were similar between the groups. Additionally, no significant differences were observed in physiological parameters (BMI, SBP, DBP, HR, CRP, and HbA1c). Conclusion: These results demonstrate that young, apparently healthy adults with a history of increased childhood adversity exhibit reduced endothelial function, an early marker of CVD development and increased CVD risk. Estimates, based on previous literature, show that a 3.9% reduction in the FMD test as observed in the high ACE group may correspond to an estimated 34% increased future CVD risk. These findings support existing literature suggesting that adversity early in life may serve as a subclinical indicator of increased risk of premature CVD potentially identifying vulnerability before traditional clinical markers emerge.