This study evaluated the relationship between adiposity, left ventricular mass and geometry, and haemodynamic parameters at rest and during laboratory stressors in a sample of 69 normotensive children with positive family histories of essential hypertension. Children were classified as overweight if they were above the 85th percentile of weight-for-height for their age and gender compared to national normative data. Nineteen children (7 whites, 12 blacks) were classified as overweight and the remaining 50 (26 whites, 24 blacks) were not overweight. Overweight children were found to have higher resting systolic and diastolic blood pressures, heart rates (HR), cardiac output (CO) and stroke volumes (SV), and lower resting total peripheral resistance than the non-overweight children. No differences were noted in haemodynamic reactivity to the stressors. Echocardiographic findings indicated that the overweight children had greater left ventricular mass indexed by height2.7, interventricular septal thickness and left ventricular end diastolic diameter (LVEDD) compared to non-overweight children. These findings are the first to indicate that the higher resting pressures of overweight normotensive children are a reflection of increased normotensive children are a reflection of increased preload (i.e. greater HR, SV, CO, LVEDD). These findings point out the early deleterious effects of obesity on the cardiovascular system in the young and highlight the need for effective obesity prevention and intervention programmes.