Aerobic capacity is important as it represents functional limits of the 02-delivery chain and is therefore an indicator of cardiovascular health. Obesity is associated with reduced cardiovascular performance and is a precursor of serious diseases. Given the importance of children’s cardiovascular health, and in light of secular trends related to height (leveled off), and weight (accelerating) current data is needed on aerobic capacity in children and youth. The purpose of this study was to examine key predictors of aerobic capacity in children and youth. The design was cross-sectional and correlational. Children ages 9-16, enrolled in 19 public schools (N=1884) were tested on the Progressive Cardiovascular Endurance Run (PACER). A multiple regression analysis examined performance on the PACER based on age, child sex, BMI, and maturation. Higher PACER scores were associated with being an older student, having a lower BMI score, and being male (all p’s<.001). In addition, there was a statistically significant gender x maturation interaction (p=.03), with early maturers performing at a lower level than late maturers – particularly for females. Conclusions. Including selected controls, children's PACER performance was explained to a considerable extent by BMI and sex, with early/late maturation also playing a significant role, particularly for females.