Objective: The aim of this study was to identify promoting and inhibiting correlates associated with the physical activity (PA) of children and adolescents (aged 3-18). The intention was to demonstrate the complexity of correlates of PA and to determine possible influencing factors. Design: A systematic review of reviews. Methods: Systematic database research was carried out in Medline, Cochrane Library, EMBASE, PsycInfo, Springer Link and Thieme Connect. Inclusion criteria were that the study: (a) was classified as a systematic review with or without meta-analysis; (b) was published between 2000 and 2009; (c) dealt with children and adolescents aged 3-18; (d) had as its dependent variable any measure of overall PA; and (e) reviewed associations between quantitatively measured variables and PA. The internal validity of the systematic reviews thus identified was evaluated using a validated quality instrument. Results: Nine systematic reviews without meta-analysis and one systematic review with meta-analysis were selected. Altogether 16 correlates were identified which were consistently associated with PA of children and/or adolescents: sex, age, ethnicity, parental education, family income, socioeconomic status, perceived competence, self-efficacy, goal orientation/motivation, perceived barriers, participation in community sports, parental support, support from significant others, access to sport/recreational facilities and time outdoors. Conclusions: Although the findings of the reviews covered are to some extent heterogeneous, it is possible to identify consistent correlates of PA in children and adolescents. The results show that PA is a complex and multi-dimensional behaviour determined by numerous biological, psychological, sociocultural and environmental factors.