Objectives: To describe the risk factors associated with injuries resulting from physical education (PE), leisure time physical activity (leisure time PA) and sports in 9-12-year-old children. Design: Prospective cohort study. Setting: Primary schools. Participants: Nine hundred and ninety-fi ve children aged 9-12 years. Main outcome measures: Injuries occurring during either PE class, leisure time PA or sports, and caused the child to at least stop the current activity were recorded prospectively. Individual weekly exposure was estimated from baseline and follow-up questionnaires. Potential risk factors were gender, age, socioeconomic status, ethnicity, habitual level of PA, body mass index and a motor fi tness. A multivariate Cox proportional hazard regression model was developed, accounting for clustering within schools. Results: Gender, age and level of PA were independent signifi cant risk factors for injury. Different modalities of PA had different injury risk factors. Most importantly, the low levels of habitual PA signifi cantly increased injury risk. Conclusions: The children at highest injury risk are the target audience of the contemporary PA promotion efforts. PA promotion should also focus on injury prevention.