Aerobic fitness, defined as maximum oxygen uptake (VO(2PEAK)), and body fat measurements represent two known risk factors for disease. The purpose of this study was to investigate the relationship between VO(2PEAK) and body fat measurements in young children at a population-based level.Cross-sectional study of 225 children (128 boys and 97 girls) aged 8-11 years, recruited from a population-based cohort. Total lean body mass (LBM), total fat mass (TBF), and abdominal fat mass (AFM) were measured by dual-energy x-ray absorptiometry. Body fat was also calculated as a percentage of body mass (BF%) and body fat distribution as AFM/TBF. VO(2PEAK) was assessed by indirect calorimetry during maximal exercise test.Significant relationships existed between body fat measurements and VO(2PEAK) in both boys and girls, with Pearson correlation coefficients for absolute values of VO(2PEAK) (0.22-0.36, P< 0.05), and for VO(2PEAK) scaled by body mass (-0.38 - -0.70, P<0.05). No relationships were detected for VO(2PEAK) scaled to LBM (-0.17-0.04, all not significant). Boys and girls in the lowest quartile according to body fat measurements had higher absolute values of VO(2PEAK) and lower values of VO(2PEAK) scaled by body mass, compared with those in the highest quartile. No differences were found for VO(2PEAK) scaled to LBM.Our findings document the coexistence of two known risk factors for disease at a young age and confirms that VO(2PEAK) was scaled to LBM may be a better, body fat independent way of expressing fitness.