Present knowledge suggests that cardiovascular disease originates and progresses from childhood and adolescence. Endothelial dysfunction is an early and crucial event in atherosclerosis.Prospective study that compares Flow Mediated Vasodilation (FMV) in children with overweight (OWC) and normal weight children. An ultrasound transducer a standard method were used to measure FMD.The study included 82 children, of whom 49 were cases (OWC) and 33 controls. FMV values ranged from -6 to 56% (x=11.1%) in OW, and from 0 to 29.6% (x=16.6%) in control children (P<.005). Paradoxical vasoconstriction was found in 34.7% in OWC as compared to nil in controls (P<.005). A significant association was found between vasoconstriction and central obesity and hypertension.The results of this study show that FMV is lower in obese compared to normal children; thus they are more likely to have endothelial dysfunction.