Notwithstanding the remarkable achievements in survival, there is a growing recognition that pediatric cancer survivors are faced with a variety of chronic health problems that may be exacerbated by maladaptive health behaviors. The purpose of the present study was to examine the utility of the theory of planned behavior (TPB) in understanding adolescent survivors' motivation to engage in physical activity. A group of adolescent cancer survivors recalled their beliefs, attitudes, norms, perceptions of control, intentions and post-treatment physical activity behaviors using a self-administered, mailed questionnaire in a retrospective design. Multiple regression analyses revealed that the TPB explained 29.1% of the variance in physical activity behavior, with the significant independent correlates being intention (beta=0.31,p=0.023) and self-efficacy (beta=0.42,p=0.04). For intention, 33.7% of the variance was explained by the TPB, with affective attitude (beta=0.32,p=0.016) and instrumental attitude (beta=0.31, p=0.037) making significant unique contributions. The present study has provided some of the first data toward understanding physical activity behavior in adolescent cancer survivors. Specifically, the results suggest that interventions designed to promote physical activity in this population should focus on the development of a positive attitude as well as fostering an enhanced sense of self-efficacy.