Primary hypertension is well known to occur in children, but the characteristics of such children are changing due to the influence of the obesity epidemic. In view of this, we conducted a cross-sectional study of 70 children [age 13.3+/-4 years (mean +/- SD)] with primary hypertension referred to a specialized pediatric hypertension clinic. Secondary hypertension had been excluded after a standardized diagnostic evaluation. Isolated systolic hypertension was present in 62.9% of subjects. Family history of hypertension was present in 86.2%, and 52.9% were obese (BMI > or =95th percentile). BMI was weakly correlated with systolic BP (r =0.28,P =0.10) and was significantly correlated with total cholesterol (r =0.36,P =0.005) and triglycerides (r =0.42,P =0.01). Mean plasma renin activity (PRA) was 3.1+/-2.7 ng/ml/h. PRA was correlated with diastolic but not systolic BP. Patients with high PRA had higher diastolic BP and lower BMI compared to those with low PRA. Left ventricular hypertrophy was present in 24%. Mean 24-h systolic BP load by ambulatory BP monitoring was 52+/-24%; mean 24-h diastolic BP load was 18+/-16%; BP loads were greater in patients with high PRA. These data suggest that primary hypertension in children is characterized by systolic BP elevation, positive family history and obesity. Hyperlipidemia accompanies primary hypertension in obese children, and left ventricular hypertrophy is common. Patients with high PRA have more severe BP elevation. Future studies should focus on further defining the pathophysiology of primary hypertension in children, including the roles of renin and insulin resistance, so that improved methods of prevention and treatment can be developed.