This study evaluated the influence of adiposity on the progression of left ventricular (LV) mass from childhood to adulthood and the relation of LV mass to insulin resistance in young adulthood. One hundred thirty-two healthy children recruited into a longitudinal study at a mean age of 13 years and reevaluated at 27 years, at which time insulin resistance studies were also performed, were studied. Echocardiographic assessment of LV mass was made and indexed for height. Body mass index (BMI) at 13 years was highly correlated with BMI at 27 years, as was LV mass index at 13 and 27 years. The cross-sectional correlation of LV mass index and BMI at 13 years (r = 0.38, p < 0.0001) had strengthened considerably by 27 years (r = 0.55, p < 0.0001). A BMI increase > or = 5.5 kg/m2 from 13 to 27 years was associated with a significantly greater increase in the LV mass index (p < 0.0001) than a BMI change < 5.5 kg/m2, and this relation was similar in children who were thin and heavy at baseline. In young adulthood, the relation of LV mass index to lean mass was weaker than that of LV mass index to fat mass. The association of LV mass with insulin resistance was dependent on adiposity. In conclusion, adiposity and LV mass are related in childhood, and this association tracks and becomes stronger in young adulthood. Moreover, the increase in LV mass from childhood to young adulthood is related to the degree of increase in BMI, independent of BMI at 13 years, suggesting that an excessive increase in LV mass could be limited by controlling gain in body fat during adolescence.