INTRODUCTION: Left ventricular hypertrophy and diastolic dysfunction in children and adolescents with essential hypertension tend to be underdiagnosed. The aims of this study were to investigate left ventricular hypertrophy and diastolic dysfunction in the subjects with essential hypertension defined by ambulatory blood pressure monitoring. METHODS: A total of 38 Korean subjects aged 9-19 years without secondary causes of hypertension were reviewed. Ambulatory blood pressure monitoring was done in the 38 subjects to diagnose hypertension and gain the information of blood pressure pattern. The subjects were divided into two groups: a group with elevated blood pressure (BP) index (n = 29) and a group with normal BP index (n = 9). Two-dimensional ultrasound with M-mode imaging and tissue Doppler imaging were performed to measure left ventricular mass index and to assess the left ventricular diastolic dysfunction. RESULTS: Left ventricular mass index(g/m(2.7)) was significantly higher in the group with elevated BP index than the group with normal BP index, but there were no differences in left ventricular diastolic dysfunction evaluated by E/A ratio and E/E' ratio. Left ventricular mass index was related only with body mass index, while any of the ambulatory blood pressure monitoring parameters did not predict left ventricular hypertrophy. In terms of diastolic dysfunction in essential hypertension, E/E' ratio in the subjects with left ventricular hypertrophy was higher than that in the other subjects without left ventricular hypertrophy. DISCUSSION: Left ventricular mass index is significantly correlated with body mass index in children and adolescents with essential hypertension, and the diastolic dysfunction could be in higher risk in subjects with left ventricular hypertrophy.