OBJECTIVE: Our aim was to investigate differences in left-ventricular mass corrected for height2.7 (LVMI) in children and adolescents according to 24-hour ambulatory blood pressure (BP) levels. METHODS: A total of 67 consecutive children and adolescents aged 5 to 20 years were analyzed. Patients underwent 24-hour ambulatory BP monitoring and echocardiography. LVMI was calculated by using the Devereux equation. All subjects underwent 24-hour ambulatory blood pressure monitoring on a usual school day. Ambulatory hypertension was defined as mean daytime systolic BP and/or diastolic BP at ≥95th percentile for gender and height (n = 22). Prehypertension was defined as mean daytime systolic BP and/or diastolic BP at ≥90th percentile and <95th percentile for gender and height (n = 13). Normotension was defined as mean daytime systolic BP and/or diastolic BP at <90th percentile for gender and height (n = 32). RESULTS: LVMI was 28.3 ± 9.4 g/m2.7 (mean ± SD) in the normotensive subjects (n = 32), whereas it was 35.1 ± 8.7 g/m2.7 in the hypertensive subjects (n = 22), a difference that was significantly higher (P < .001, Mann-Whitney test). LVMI was 32.4 ± 5.4 g/m2.7 in prehypertensive subjects (n = 13), values that tended to be lower than the values of hypertensive subjects (P = .275) and significantly higher than the values of normotensive subjects (P < .05, Mann-Whitney test). CONCLUSIONS: Children and adolescents characterized as hypertensive or prehypertensive using the ambulatory blood pressure criteria exhibited significantly higher LVMI than normotensive subjects. Prehypertensive children may be at a similar risk for cardiovascular target-organ damage as that established for hypertensive children.