PURPOSE: To determine if adult survivors of childhood acute lymphoblastic leukemia (ALL) are less active (and more inactive) than the general population and to identify modifying factors. PATIENTS AND METHODS: Physical activity was assessed by self-report in 2,648 adult survivors of the Childhood Cancer Survivor Study. Participants in the Behavioral Risk Factor Surveillance System (BRFSS) survey administered through the Centers for Disease Control and Prevention (CDC) were used as a comparison group. RESULTS: Survivors had a mean age of 28.7 years (range, 18.0-44.0 years) and were a mean of 23.1 years from their cancer diagnosis (range, 16.0-33.8 years). In multivariate models, ALL survivors were more likely to not meet CDC recommendations for physical activity [odds ratio (OR), 1.44; 95% confidence interval (95% CI), 1.32-1.57] and more likely to be inactive (OR, 1.74; 95% CI, 1.56-1.94) in comparison with the BRFSS general population. Survivors treated with >20-Gy cranial radiotherapy were at particular risk. Compared with BRFSS participants and adjusted for age, race, and ethnicity, survivors were more likely to not meet CDC recommendations (females: OR, 2.07, 95% CI, 1.67-2.56; males: OR, 1.43, 95% CI, 1.16-1.76) and more likely to be inactive (females: OR, 1.86; 95% CI, 1.50-2.31; males: OR, 1.84; 95% CI, 1.45-2.32). CONCLUSIONS: Long-term survivors of childhood ALL are less likely to meet physical activity recommendations and more likely to report no leisure-time physical activity in the past month. This level of inactivity likely further increases their risk of cardiovascular disease, osteoporosis, and all-cause mortality.