Little is known about the association between physical activity and lung function in childhood. We conducted a survey including parental reports of the child’s participation in physical activity and measurements of lung function. The associations between physical activity and lung function were estimated by linear regression analysis adjusting for potential confounders in 2,537 children (9 to 10 years). Using the linear model in exploring the effect of physical activity on lung function with those who were physical active less than once a week as the reference category, showed that forced expiratory volume in 1 s (FEV1) was highest among those who were physical active ≥ 4 times a week also when adjusting for potential confounders (p = .02). FEV1 increased with 70 ml. A similar pattern was present for forced vital capacity (FVC; p = .002). The present tudy suggested that lung function was highest in highly physical active children age 9 to 10 years. The implications are that exercise may influence lung function, but these findings need to be confirmed using a longitudinal study design.