Hypertension is an under-recognized clinical entity in children. Blood pressure (BP) assessment should be one of the routine examinations in childhood and adolescence. Many particular features characterize hypertension in children: optimal BP determination in children requires the use of an appropriately sized cuff and BP measurement must be repeated for confirmation. The definition of hypertension is based on the normative distribution of BP in healthy children according to gender, height and age. It is graded to distinguish mild hypertension from confirmed or severe hypertension. Ambulatory BP monitoring may facilitate detection of borderline hypertension and treatment monitoring. Careful clinical assessment is the key for identifying predisposition to primary adult hypertension or secondary causes. Target organ abnormalities, additional cardiovascular risk factors and comorbidities have to be taken into account. High BP in childhood and primary hypertension have to be considered as risk factors for cardiovascular disease in early adulthood. Secondary hypertension is common in children with confirmed or severe hypertension and screening test should be individualized for each child. Renal or renovascular causes concern a majority of children but aortic coarctation or endocrine diseases can also be found. Symptomatic children and patients with severe hypertension require antihypertensive drug therapy. Lifestyle modifications including diet exercise and reduction of overweight remain the basic principles of the treatment in mild hypertension.