Elevated C-reactive protein (CRP) levels have been associated with increased cardiovascular risk in hypertensive adults. The aim of this study was to determine whether plasma CRP level is more predictive of left ventricular hypertrophy (LVH) than is ambulatory blood pressure (BP) in hypertensive children. Baseline and 12-month follow-up measures of BP, body mass index (BMI), low-density lipoprotein/high density lipoprotein cholesterol, left ventricular mass (LVM), and CRP data collected from 48 newly diagnosed, untreated hypertensive children were analyzed. CRP was measured by a highly sensitive nephelometric method. Left ventricular mass index (LVMI) was calculated as LVM/height(2.7), and LVH was defined as LVMI > 38.6 g/m(2.7) being the cut-point for the 95th percentile found in healthy children. Average systolic BP (SBP), diastolic BP (DBP), SBP index, and DBP index were calculated. All patients received hydrochlorothiazide therapy in combination with angiotensin converting enzyme inhibitor treatment. Five patients also had angiotensin receptor blocker therapy to reach the target BP (< 95th percentile corrected for age and gender). In a multiple regression analysis, LMVI was correlated with CRP, BMI, SBP, and SBP index. CRP alone explained 77% of the variance of LVMI, whereas BMI, SBP, and SBP index explained only 1.3, 0.3, and 0.4% of the variance, respectively. CRP was also the most significant correlate of follow-up LVH. In conclusion, elevated CRP level is significantly associated with LVH in children with essential hypertension. BP reduction with renin-angiotensin system blocker and hydrochlorothiazide therapy reduces LVH while lowering CRP level.