The International Consensus Conference on Physical Activity Guidelines for Adolescents convened to review the effects of physical activity on the health of adolescents, to establish age-appropriate physical activity guidelines, and to consider how these guidelines might be implemented in primary health care settings. Thirty-four invited experts and representatives of scientific, medical, and governmental organizations established two main guidelines. First, all adolescents should be physically active daily or nearly every day as part of their lifestyles. Second, adolescents should engage in three or more sessions per week of activities that last 20 min or more and that require moderate to vigorous levels of exertion. Available data suggest that the vast majority of U.S. adolescents meet the first guideline, but only about two thirds of boys and one half of girls meet the second guideline. Physical activity has important effects on the health of adolescents, and the promotion of regular physical activity should be a priority for physicians and other health professionals.