The present study examined the efficacy of a theory-based intervention designed to positively influence physical activity (PA) behavior in a group of pediatric cancer survivors. Ten survivors participated in a 16-week PA intervention that targeted the main theoretical tenets of the theory of planned behavior (TPB). Survivors were followed over a course of 1 year and completed measures of attitudes, subjective norms, perceived control, intentions for PA, and self-reported PA behavior at five different times. While the magnitude of change varied across the key theoretical constructs, it appears that the intervention had a small yet meaningful impact, particularly for overall behavioral intentions. Overall, this study provides preliminary data to suggest that the TPB may be a viable framework from which to build interventions for pediatric cancer survivors. Future research will be required to further identify and target the key elements and theoretical constructs within a behavioral intervention.