The most frequent cause of hyperthyroidism in children is Graves’ disease (GD). Vascular endothelium is a specific target of thyroid hormone. The purpose of this study is to assess flow-mediated dilatation (FMD)% and serum von Willebrand factor (vWF) levels in children with newly diagnosed GD to reflect the extent of endothelial dysfunction in those children. In this study, 40 children with newly discovered GD and 40 children who were healthy served as the control group. Both patients and controls had anthropometric assessment, as well as measurements of fasting lipids, glucose, insulin, high-sensitivity C-reactive protein (hs-CRP), TSH, and free thyroxine (FT4 and FT3), thyrotropin receptor antibodies TRAbs and vWF. Noninvasive ultrasound was utilized to quantify the carotid arteries’ intima-media thickness and the brachial artery’s FMD. Patients reported significantly reduced FMD response and greater vWF and hs-CRP levels compared to controls (P= 0.001 for each). In multivariate analysis, we reported that vWF was significantly correlated with TSH (OR 2.5, 95% CI 1.32–5.32,P= 0.001), FT3 (OR 3.4, 95% CI 1.45–3.55,P= 0.001), TRAb (OR 2.1, 95% CI 1.16–2.23,P= 0.01), and FMD% (OR 4.2, 95% CI 1.18–8.23,P= 0.001).Conclusions: Children with newly diagnosed GD have endothelial dysfunction, which is shown by impaired FMD and increased vWF. These findings support the idea that GD may need to be treated as soon as possible.What is Known:• Graves' disease is the most common cause of hyperthyroidism in children.• vWF is a reliable marker for detection of vascular endothelial dysfunction.What is New:• Children with newly diagnosed Graves' disease may have endothelial dysfunction as reflected by impairment of FMD and raised vWF level.• Measurement of vWF level in children with newly diagnosed Graves' disease can be used for early detection of endothelial dysfunction.