AIM: Prehypertension has recently been observed as a potent cardiovascular risk factor. Though prehypertension has a strong familial predisposition, the pathophysiological mechanisms that cause its progression to prehypertension in normotensive sibling of hypertensive parents have not yet been fully elucidated. Therefore, the present study was conducted in normotensive and prehypertensive sibling by spectral analysis of heart rate variability (HRV) to understand the nature of change in sympathovagal balance (SVB) in this condition. METHODS: Body mass index (BMI), waist circumference (WC), waist-hip ratio (WHR), basal heart rate (BHR), blood pressure (BP), rate pressure product (RPP) and spectral indices of HRV were assessed in three groups of subjects: Group I (normotensive offspring of normotensive parents, N.=231); Group II (normotensive offspring of hypertensive parents, N.=113); and Group III (prehypertensives offspring of hypertensive parents, N.=52). SVB was analyzed and correlated with BMI, WHR, BHR, BP and RPP in all the groups. RESULTS: Sympathovagal imbalance (SVI) was observed to be present in both normotensive and prehypertensive sibling of hypertensive parents. In normotensive sibling, SVI was mild in the form of proportionate increase in sympathetic and decreased vagal activity. In prehypertensive sibling, SVI was prominent with more of vagal withdrawal. Though LF-HF ratio, the indicator of SVB was correlated with all parameters in groups II and III, the significance was more with diastolic pressure and WHR. CONCLUSION: It was concluded that vagal inhibition plays a critical role in modulation of SVB for progression into prehypertension in normotensive sibling of hypertensive parents and WHR is a prominent marker of SVI in these subjects.