Abstract Background and Objective: Obesity is an important risk factor for development of hypertension. We investigated the association between body mass index (BMI) and blood pressure in adolescents. Methods: The cross-sectional study was performed on 694 adolescents aged 12-18 years from middle and high schools located in 4 districts of Shiraz, Iran. Height, weight, and systolic and diastolic blood pressures were measured according to standard procedures. Results: The prevalence of overweight/obesity and elevated systolic and diastolic blood pressure was 22.0%, 16.8%, and 13.3%, respectively. Compared to girls, boys had higher rates of overweight/obesity and elevated blood pressure. With increasing age, the prevalence of overweight decreased (20.6% in 15-18 years compared to 34.3% in 12-14 years) and that of elevated blood pressure increased (33.2% vs.14.6% for systolic and 22.2% vs. 10.3% for diastolic blood pressure) in boys whereas the prevalence of overweight/obesity and elevated blood pressure did not change among girls. In both sexes, elevated blood pressure had a positive association with BMI categories independent of age and this association was observed even in normal versus low BMI categories. Conclusion: A strong association between BMI and elevated blood pressure advocates using strategies for the control of weight and prevention of obesity in adolescents.