Objectives: To determine the influence of essential arterial hypertension on the systemic micro- and macrovascular endothelial response, on cerebral hemodynamics and on the level of oxidative stress and targeted proinflammatory markers in the pediatric population. Study design: the study was designed as a cross-sectional observational trial in which all subjects were subjected to the same experimental protocol. The subjects were divided into two groups according to the (non)existence of essential arterial hypertension. Participants and methods: a total of 52 participants, children and adolescents, of both sexes, aged between 9 and 17 years, participated in the study, divided into the NT group (N = 26), which was composed of healthy children and adolescents with normal arterial blood pressure values, and the HT group (N = 26) which included children and adolescents suffering from essential arterial hypertension. Endothelial microvascular function was evaluated in response to vascular occlusion (PORH), iontophoretic application of acetylcholine (AChID) and sodium nitroprusside (SNPID) and local thermal skin hyperemia (LTH), and in macrocirculation by measuring flow-mediated dilation (FMD) of the brachial artery. Cerebral circulation was assessed using transcranial doppler (TCD) and the intima-media thickness of the common carotid artery was measured to all subjects. Serum concentrations of biomarkers of oxidative stress and antioxidant capacity were measured using standardized methods. The subjects' eating habits were assessed by using a questionnaire on the frequency of food intake. Anthropometric, hemodynamic and biochemical measurements were performed on all subjects, and the status of body fluids was measured. Results: Although hypertensive subjects had higher values of systolic, diastolic and mean arterial pressure and higher BMI than normotensive subjects, heart rate and waist-to-hip ratio were similar in both groups. In addition, children and adolescents with essential arterial hypertension had significantly higher serum total and LDL cholesterol levels, as well as markers of the acute phase of inflammation (CRP, fibrinogen, ferritin) and oxidative stress (8-isoPGF2α) than normotensive subjects. Essential arterial hypertension significantly reduced endothelium-dependent vasodilation in microcirculation (PORH, AChID, LTH) and macrovasculature (FMD), while it had no significant effect on endothelium-independent 9. SUMMARY 58 microvascular vasodilation (SNPID). Flow velocities in the right MCA were increased in hypertensive subjects compared to healthy normotensive subjects, as well as the thickness of the intima-media of the right common carotid artery. Conclusion: Essential arterial hypertension has an unfavorable effect on endotheliumdependent vasodilatation in the micro- and macrocirculation of children and adolescents, regardless of BMI. It is accompanied by increased flow rates in the cerebral circulation and increased thickness of the intima-media of the common carotid artery. Underlying this functional vascular damage are an elevated serum levels of oxidative stress and increased proinflammatory parameters.