High blood pressure in children and adolescents may have an adverse impact on the heart, the vessels, the kidney, and the central nervous system causing early functional or structural changes. The most prevalent subclinical hypertensive target organ damage in children and adolescents is left ventricular hypertrophy, and echocardiographic assessment of left ventricular mass is suggested in all hypertensive children. There is evolving evidence that antihypertensive treatment in children and adolescents could lead to regression of target organ damage, emphasizing also the importance of adequate blood pressure control. Assessment of subclinical organ damage could guide clinical decisions from diagnosis with regard to intensity non-pharmacological treatment, time to wait for initiation of pharmacological treatment, and choice of drug. Longitudinal studies are needed to relate the effectiveness of antihypertensive treatment and blood pressure targets in childhood with future cardiovascular or renal events. This review summarizes evidence on the associations of hypertension with target organ damage in children and adolescents and the role of antihypertensive therapy on the regression of target organ damage in the pediatric age group.