Left ventricular (LV) mass has been established as an independent risk factor for cardiovascular disease morbidity and mortality. To account for differences in body size, a variety of factors have been proposed for indexing LV mass. Dual energy x-ray absorptiometry provides a measure of lean body mass which can be used as a comparison with other more clinically applicable methods of standardization. The study included 192 subjects (100 male, 103 white) aged 6 to 17 years. Lean body mass was determined by dual energy x-ray absorptiometry and LV mass was calculated from M-mode echocardiographic measurements. There were significant differences by gender (males 98.7 g, females 80.3g, p < 0.001), but not race, for unindexed LV mass. Indexing LV mass by lean body mass eliminated the difference by gender. Log-log regression analysis revealed that the optimal height exponent for indexing LV mass was height³ (95% confidence interval, 2.8 to 3.1). LV mass/height³ provided the most consistently high intraclass correlation with LV mass/lean body mass versus indexing with body surface area, height, height², and height^2.7 across the 4 race/gender groups. LV mass indexed by height³ eliminated differences in LV mass by gender (males 26.1 ± 4.72 g/m³, females 25.5 ± 4.8 g/m³, p = NS). The proposed method for indexing LV mass by height³ should be useful in the clinical setting. The 90th and 95th percentiles of LV mass/height³ provide cutpoints for determining the presence of LV hypertrophy in children and adolescents.