Objective This study evaluated associations between social, environmental, demographic, and medical predictors, and child and adolescent survivors' physical activity (PA). Methods A structured telephone survey was conducted with 105 caregiver-survivor (aged 8-16 years) pairs and 36 caregivers of younger survivors (aged 6-7 years) alone. Participants completed Measures assessing survivor PA and proposed predictors of PA including demographic, medical, social, and environmental influences. Results Social influences, including family PA, family support for PA, and peer support for PA, emerged as unique predictors of survivor PA. These variables predicted PA after controlling for demographic and medical factors. Child survivors' PA was more strongly predicted by family influences while adolescent survivors' PA was more strongly influenced by family and peer influences. Conclusions Child and adolescent survivors' PA is strongly influenced by social factors. This finding parallels Results with healthy children. PA interventions should focus on family and peer support to increase survivors' PA behaviors. © 2011 The Author.