The relation between 24-h ambulatory blood pressure monitoring and echocardiographic left ventricular (LV) anatomy and function was examined in 30 young, normotensive offspring (16 men, 14 women) of hypertensive, parents and in 20 offspring (12 men, 8 women) of normotensive parents, comparable for age, clinical blood pressure, and gender. Offspring of hypertensive subjects exhibited higher body mass index (P < .01), relative wall thickness, and LV mass/height (both P < .001). No significant difference was found in LV chamber dimensions and in either systolic or diastolic function. The 24-h systolic and diastolic blood pressures were higher in offspring of hypertensive subjects than in controls (P < .001 and P < .0001, respectively), as was the coefficient of variation of 24 h systolic blood pressure (P < .01). In pooled groups, LV mass was positively related to daytime systolic blood pressure (r = 0.48), daytime diastolic blood pressure (r = 0.47) (both P < .001), and the coefficient of variation of 24 h diastolic blood pressure (r = 0.37, P < .01). In a multiple regression model, including as variables, body mass index, daytime systolic and diastolic blood pressures, male gender, and family history of hypertension were the major independent predictors of LV mass (both P < .0001), with an additional contribution of the coefficient of variation of 24 h diastolic blood pressure (P < .05). We conclude that male gender and a family history of hypertension are stronger determinants of early changes in cardiac structure than hemodynamic load in a group of young, normotensive adults.