Primary hypertension in children has become common with the rise in prevalence of childhood obesity. The mechanisms underlying obesity-induced high blood pressure are unclear. Leptin is known to play a role in the pathophysiology of obesity. We examined obese children to look for a relationship between leptin and blood pressure. Children from all the primary schools of the 6th region of Tehran were screened for obesity. Anthropometric measurements were done, and blood samples for the measurement of serum leptin were collected from 515 obese children. Children were divided into normotensive and hypertensive groups and serum leptin levels were compared. The median serum leptin level for all obese children was 9.80 ng/mL (5.00-14.40 ng/mL). There was no significant difference in leptin levels between hypertensive and normotensive groups. In both groups, serum leptin levels were significantly correlated with body mass index (BMI) and systolic, but not diastolic, blood pressure. In the multivariate linear regression model constructed by age, sex, BMI, and leptin as independent variables, leptin was not an independent predictor of systolic or diastolic blood pressure. Although leptin was correlated with blood pressure in a univariate analysis, it lost its predictive power after adjustment for other important variables, especially BMI. It seems unlikely that plasma leptin is a mediator of hypertension in obese children.