The objective of this review was to systematically synthesize the results of original studies on the association between physical activity and social support in adolescents, published until April 2011. Searches were carried out in Adolec, ERIC, Lilacs, Medline, SciELO, Scopus, SportsDiscus and Web of Science electronic databases and the reference lists of selected articles. Searches for articles, data extraction and assessment of methodological quality were conducted independently by two reviewers. In total, 75 articles met inclusion criteria and were analyzed. Most studies were published over the past 6 years (2006-11), conducted in high-income countries, with a cross-sectional design, using subjective measures of physical activity (e.g. questionnaires and recall) and exhibited medium to high methodological quality level. Social support was positive and consistently associated with the physical activity level of adolescents in cross-sectional and longitudinal studies. Those who received more overall social support as well as support from both parents, friends and family showed higher levels of physical activity. It is concluded that social support is an important factor associated with physical activity level in adolescents and should be targeted in intervention programs that aim to increase physical activity levels in this population group.