Background: Childhood cancer survivors (CCS) are at high risk of developing treatment-related late effects, including cardiovascular disease and diabetes, which can be exacerbated by inadequate physical activity (PA). Relationships between PA, physical fitness, and cardiometabolic risk factors in CCS have not been well described. Furthermore, active transportation, a specific domain of PA, has not been previously studied in CCS. The primary aims of this dissertation were to examine associations between PA/fitness and cardiometabolic risk factors and to identify active transportation behaviors and barriers in CCS.Methods: In Project 1, associations between PA and cardiometabolic risk factors were examined in 319 CCS and 208 sibling controls aged 9-18 years. In Project 2, associations between PA/fitness and cardiometabolic risk factors were examined in 119 adult CCS with a history of hematopoietic cell transplantation and 66 adult sibling controls. In Project 3, we recruited 158 adult CCS and 153 controls matched on age, sex, and location to complete a survey regarding active transportation behaviors and perceptions. Linear and logistic regression models accounting for correlation among siblings or matched participants were used to address research questions.Results: Higher levels of PA in CCS aged 9-18 (Project 1) and higher levels of endurance in adult CCS (Project 2) were associated with a favorable cardiometabolic profile. In Project 3, adult CCS engaged in similar levels of active transportation as controls despite perceiving greater health-related barriers. Marital/relationship status, planning/psychosocial barriers, and perceived neighborhood walkability were the strongest correlates of active transportation among CCS, while objective neighborhood walkability was the strongest correlate among controls.Conclusions: Findings suggest that efforts to increase PA and endurance in CCS may reduce the risk of future cardiovascular disease. Interventions might consider promoting active transportation as a moderate intensity PA option, since it appears to be as well accepted in CCS as in healthy adults. Such interventions will not be successful, however, without existing or improved pedestrian and bicycle infrastructure, safety, and access to local amenities. Additional research is needed to confirm results and explore the feasibility and efficacy of active transportation interventions in this population.