Physical activity in adolescence may contribute to the development of healthy adult lifestyles, helping reduce chronic disease incidence. However, definition of the optimal amount of physical activity in adolescence requires addressing a number of scientifIc challenges. This article reviews the evidence on short- and long-term health effects of adolescent physical activity. Systematic reviews of the literature were undertaken using a reference period between 2000 and 2004, based primarily on the MEDLINE/PubMed database. Relevant studies were identifIed by examination of titles, abstracts and full papers, according to inclusion criteria defined a priori. A conceptual framework is proposed to outline how adolescent physical activity may contribute to adult health, including the following pathways: (i) pathway A — tracking of physical activity from adolescence to adulthood; (ii) pathway B — direct influence of adolescent physical activity on adult morbidity; (iii) pathway C — role of physical activity in treating adolescent morbidity; and (iv) pathway D — short-term benefits of physical activity in adolescence on health. The literature reviews showed consistent evidence supporting pathway ‘A’, although the magnitude of the association appears to be moderate. Thus, there is an indirect effect on all health benefits resulting from adult physical activity. drawing recommendations. Finally, although studies on physical fitness are of interest for understanding the relationships between fitness and health, guidelines should focus on PA rather than fitness. Definition of adolescent PA guidelines is beyond the scope of this article, but our conceptual framework, and the recognition that domains of PA are different from those of adults may help governmental and non-governmental agencies involved in creating these guidelines.