Background Current blood pressure (BP) classification is based on the recent recommendations of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure (JNC-7) and the 2003 European Society of Hypertension–European Society of Cardiology Guidelines for the Management of Arterial Hypertension. The JNC-7 introduced a new concept, prehypertension, and recommended health-promoting lifestyle modifications for these individuals. Obesity is also recognized as a major risk factor for the development of hypertension. We aimed to determine the prevalence of hypertension and obesity in a large cohort of adolescents and to assess whether prehypertension and body mass index (BMI) increase with increasing age. Methods A cross-sectional population-based study was performed using data collected during 1996 to 2002 in an army recruitment examination of 560,588 Israeli individuals 16.5 to 19 years of age. The subjects were divided according to gender and stratified by increasing 6-month intervals into five groups. Prehypertension was defined as BP 120 to 139 / 80 to 89 mm Hg. Overweight was defined as BMI 25 to ≤30 and obesity as BMI >30 kg/m 2. Results Mean systolic BP (SBP) and diastolic BP (DBP) were significantly higher in male subjects for all groups. By applying the JNC-7 criteria, 56.8% of male subjects and 35.8% of female subjects would be considered prehypertensive. There was a statistically significant increase in the mean SBP and DBP with age and BMI. Among male subjects 10.9% were overweight and 3.3% were obese; among female subjects, 11.1% were overweight and 3.2% were obese. The BMI did not increase with increasing age. The prevalence of prehypertension was significantly higher in obese subjects. Conclusions Prehypertension is very common among Israeli adolescents. A substantial number of adolescents exhibit a BMI greater than normal. As both of these factors are known to be asssociated with increased cardiovascular risk, early institution of healthful lifestyle changes in a large proportion of this age group is recommended.