The need for calculations limits the clinical use of left ventricular (LV) mass. Because LV mass is strictly dependent on wall thickness for every given value of LV external dimension, we tested the clinical value of the sum of LV external dimension plus ventricular septal thickness plus posterior wall thickness as predictors of standard LV mass. We studied 295 healthy normotensive subjects and 1,686 subjects with systemic hypertension, followed up for 1 to 9 years. In the normotensive group, the predictor of LV mass showed a very close association with standard LV mass according to an allometric model (LV mass [g]=0.230×LV mass predictor [cm]^3.01), with 99.7% of LV mass variability explained by the model. Also, in the hypertensive group, the LV mass predictor showed a very close allometric relation to standard LV mass (R² = 0.998). During follow-up there were 154 cardiovascular morbid events and 50 deaths from all causes. The risk of cardiovascular morbid events and that of death increased to a similar extent with LV mass normalized by body surface area, height or height^2.7, as well as with the LV mass predictor. The risk estimates for cardiovascular morbidity and all-cause mortality provided by models including either LV mass predictor or LV mass uncorrected or corrected by height, body surface area, or height^2.7 did not show any statistical differences between the different models. In conclusion, the sum of LV external dimension plus ventricular septum thickness plus posterior wall thickness, easily measurable from the M-mode echocardiographic tracing, very closely predicts standard LV mass in adult hypertensive subjects. The prognostic value of this measure does not differ from that of standard LV mass.