The relationship between blood pressure and anthropometric or metabolic factors was studied in 324 obese children aged 9.5 +/- 1.8 years (mean +/- standard deviation). Obese children had a significantly higher blood pressure than non-obese children (systolic blood pressure: 121 +/- 14 mmHg in obese children vs 112 +/- 11 mmHg in non-obese children, P less than 0.001; diastolic blood pressure: 72 +/- 9 mmHg in obese children vs 66 +/- 7 mmHg in non-obese children, P less than 0.001). When the obese children were divided into hypertensive and normotensive groups, there was a significant difference in fasting serum insulin levels between the two groups (19.3 +/- 9.3 microU/ml in the hypertensive group vs 13.0 +/- 6.1 microU/ml in the normotensive group), and a close correlation between fasting serum insulin levels and systolic blood pressure was demonstrated (r = 0.63, P less than 0.001). However, there was no significant correlation between blood pressure and the degree of obesity itself or the waist-to-hip ratio in the obese children. There was no significant correlation between blood pressure and fasting plasma glucose, serum total cholesterol, or triglycerides levels in the obese children. Moreover, the correlation between fasting insulin levels and blood pressure was shown to be independent of the degree of obesity or waist-to-hip ratio and age by multiple regression analysis. These results indicate that hyperinsulinemia itself may play an important role in the pathogenesis of hypertension in obese children.