OBJECTIVE: To see whether concerns about injury risk relate to children's physical activity (PA). METHODS: Two cohorts were recruited from 19 Australian schools and assessed in 2001 (T1), 2004 (T2) and 2006 (T3). The younger (n=162) was assessed at 6, 9 and 11years old, and the older (n=259) at 11, 14 and 16 years old. At T1 and T2, parents of the younger cohort reported on fear of child being injured, and whether child would be at risk of injury if they played organised sport; the older cohort self-reported injury fear. Accelerometers assessed PA at each time point. Linear regression models examined cross-sectional associations, and also associations between T1 injury fear and risk and T2 PA, and T2 injury fear and risk and T3 PA. RESULTS: In the younger cohort at T2 (9 years), fear and risk were both negatively associated with moderate to vigorous PA (MVPA) (β=-0.17, 95% CI -0.30 to -0.03 and β=-0.26, 95% CI -0.41 to -0.10) and also vigorous PA (VPA). Fear was also associated with moderate PA (MPA). For the older cohort at T1, injury fear was negatively associated with MVPA (β=-0.21, 95% CI -0.35 to -0.07) and also MPA and VPA. Parental perception of risk at T1 (6 years) was negatively associated with children's MPA at T2 (9 years) (β=-0.17, 95% CI -0.32 to -0.02). Sex did not moderate any association. CONCLUSIONS: Younger children and their parents need to know which sports have low injury risks. Some children may need increased confidence to participate.