Hypertension may lead to irreversible damages in vital organs, such as heart, brain, and kidney, and may cause death in children if treatments are not given despite early diagnosis. This cross-sectional epidemiological study was conducted during 1 January-31 March 2004 to investigate the prevalence of hypertension among high school students. The study cohort included 1,041 students of six high schools, who were selected from among 14,789 students of 26 high schools in Sivas province of Turkey, using the cluster-sampling method. A questionnaire was used for collecting information from students on age, gender, smoking, and whether they or their families have any diseases. Blood pressure, height, and weight of the participitants were determined by the research group. Students whose repeated systolic or diastolic blood pressures were higher than the 95th percentile were considered to be hypertensive patients. Hypertension was prevalent among 4.4% (n=45) of the students. There was a significant correlation between prevalence of hypertension and body mass index. No significant correlation was found between prevalence of hypertension and other variables, such as smoking, age, gender, and family history of diabetes. The results suggest that hypertension is an important public-health problem among high school students. The results also showed that the body mass index was an important parameter in hypertension in such a study group. Researchers should consider overweight a causative risk factor for development of hypertension in early-onset groups.