The relationship between adiposity and cardiac dimensions were considered in healthy 9- to 18-year-old boys (n=198) and girls (n=154). Indicators of adiposity included the body mass index (BMI), sum of skinfolds (SSF) and trunk-to-extremity ratio (TER). The following left ventricular (LV) dimensions were measured by echocardiography: internal diameter (LVIDd); posterior wall thickness (PWT) and intraventricular septal wall thickness. LV mass (LVM) was estimated. In boys, 11 of 45 correlations were significant. The magnitude of the correlations increased across age groups and most of the correlations were significant in the oldest age group. In girls, 18 of 45 correlations were significant, but there were inconsistent patterns in the magnitude of the correlations across age groups. Correlations between BMI and LVIDd and LVM were highest in youth 13-15 years, whereas other correlations involving the BMI were rather constant across age groups. Correlations involving SSF were significant only in 9-12 and 13-15 year olds. There were no significant correlations involving TER in female subjects. In the total sample of boys, only correlations between the BMI and LV parameters were significant (r=0.14-0.38), except for the relationship between SSF and PWT (r=0.21). The TER was weakly associated with LV parameters. In the total sample of girls, correlations for LV parameters were significant for both the BMI (r=0.20-0.43) and SSF (r=0.18-0.28; except for LVIDd). TER was not significantly related to LV parameters except LVIDd (r=0.16). The findings indicate that the BMI is an important determinant of LV structure.