The ability to identify the hypertensive patient who is destined to suffer a morbid or fatal complication in the long presymptomatic phase of this condition, when its natural history would be most subject to amelioration, is limited by the weak relation between the level of blood pressure and the occurrence of complications. Recent research indicates that the level of left ventricular (LV) mass--most conveniently measured by echocardiography--reflects the combined effects of a variety of factors involved in the pathophysiology of hypertension, including obesity, exaggerated blood pressure responses to everyday activity, high sodium intake and blood viscosity, and genetic factors predisposing to hypertension. Prospective studies indicate that LV mass is a stronger predictor of subsequent morbid events and death than blood pressure or other conventional risk factors except age. Preliminary findings of close relations between LV mass and arterial disease and between the change in LV mass during antihypertensive treatment and subsequent events contribute to explaining the strong predictive value of LV mass. Further research is needed to clarify the biologic basis of these observations and to determine whether stratification of hypertensive patients based on their level of LV mass can improve the treatment of hypertension.