Purpose: To describe motor function and participation in, barriers to, and preferences for physical activity (PA) in adolescents during and after treatment of cancer and to discuss PA promotion in the context of developmental and cancer transitions. Method: A cross-sectional survey study used the Transfer and Basic Mobility and Sports/Physical Functioning self-report and parent-report scales of the Pediatric Outcomes Data Collection Instrument (PODCI) and questions about PA participation and preferences to collect information from 80 adolescents and 63 parents. Results: PODCI scores for adolescents receiving treatment were more variable and significantly lower than those of adolescents who had been off treatment for more than 2 years. Fatigue, pain, general health, and doctor's orders were frequently identified as barriers to PA for adolescents receiving treatment. Many did not achieve recommended levels of PA. The adolescents expressed preferences for being active with friends and family, at home or in school, in the afternoon or evening, and through daily recreational and sports activities typical of teenagers. Conclusions: Physical abilities and participation in and barriers to PA vary across the cancer journey. Interventions should be sensitive to variability and acknowledge individual preferences and environments throughout the trajectories and transitions of cancer treatment and youth development to achieve lifelong healthy lifestyles.