Arterial hypertension constitutes a significant clinical problem in everyday medical practice. It mainly concerns adult patients, but can also develop in childhood and adolescence. The diagnosis of hypertension in children and adolescents is possible by the systematic measurement of blood pressure levels during routine visits (observing the principles concerning the adequacy of measurements) and by referring the values to biological norms (blood pressure percentile tables) and applying proper definitions. Arterial hypertension in children and adolescents can be essential (primary), but much more frequently (compared with adults), it is secondary to a disease of other organs and systems. The predominant secondary causes of hypertension in children and adolescents are renal parenchymal and vascular pathologies, which must be considered in the diagnostic process. Additional examinations conducted in a patient with arterial hypertension depend on the child’s age, severity of hypertension, history and physical findings. Examinations to evaluate the advancement of target organ complications should be conducted simultaneously with the diagnostic process conducted to determine the aetiology of hypertension. A diagnosis of arterial hypertension in the developmental age makes it possible to implement an adequate therapy by treating the underlying condition, modifying patient’s lifestyle or prescribing pharmaceutical agents. The goal of an effective therapy is to prevent early and late complications of hypertension and reduce the risk of hypertensive emergencies.