Objective: The prevalence of hypertensive disease among adolescents is increasing trend. This rise in hypertension (HTN) among adolescents is multifactorial. Prehypertension advances to HTN in due course in adult life, becoming one of the major risk factors for cardiovascular diseases later. We aim to determine the prevalence of prehypertension among adolescents in Tirunelveli town. Methods: One thousand high school children aged 14–18 years from Tirunelveli city were chosen. The blood pressures (BPs) (systolic and diastolic) were recorded using the standard technique. Physical biometrics was documented. Results: BP >90th percentile is considered to be abnormal in adolescents. Prevalence of prehypertension is 0.7% (f-0%, m-0.7%), HTN is 4.7% (f-2.5%, m-2.2%), and cumulative abnormal BP is 5.4%. Among the 54 adolescents, only one had body mass index of overweight category surprisingly. Conclusion: Previous studies indicate approximately 3–4% of adolescents develop consistently elevated BP across many countries. The common causes attributed are physical inactivity, consumption of junk food, besides hormonal changes in adolescents. The results of our study indicate 5.4% of students having more than the 90th percentile nearly corresponds to results of many studies. Early detection of prehypertension in adolescents is cost-effective measure that would further avoid impoverishment to the middle-income group as well as improve the quality and expectancy of life. Effective specific school health programs are needed at the time, especially in developing countries like India.