Three national health objectives for 2010 (objectives no. 22-6, 22-7, and 22-11) aim to increase levels of physical activity and reduce sedentary behavior among children and adolescents. To promote a healthy, more active lifestyle among U.S. youth, CDC developed the Youth Media Campaign (YMC), a national initiative to encourage children aged 9-13 years to engage in and maintain high levels of regular physical activity. To provide a baseline assessment of physical activity levels among children aged 9-13 years, CDC conducted the YMC Longitudinal Survey (YMCLS), a nationally representative survey of children aged 9-13 years and their parents. This report presents data from the survey, which indicate that 61.5% of children aged 9-13 years do not participate in any organized physical activity during their nonschool hours and that 22.6% do not engage in any free-time physical activity. Improving levels of physical activity among this population will require innovative solutions that motivate children and that address parents' perceived barriers to their children engaging in physical activity.