Inactivity is an epidemic among adolescents; underscoring a critical need for action. The aim of this study was to investigate physical activity (PA) participation, sedentary behaviour, physical health, correlates of PA and physical activity enjoyment. The Children’s Sports Participation and Physical Activity Study (2010) used a self-report questionnaire to measure PA participation, sedentary behaviour and demographic, psychological and environmental variables. Physical health measures were aerobic fitness, BMI, waist circumference and blood pressure (BP). Over five thousand adolescents participated in the CSPPA study (N=5397, mean age=13.85 ± 1.97, 10-18 years, 47% male). Males had a higher average of days of MVPA ≥60 per week minutes than females. Females engaged in more social/school based sedentary activities while males engaged in more technological sedentary activities. Activity decreased and sedentary behaviour increased with age. Sedentary behaviour decreased with increasing participation in all forms of physical activity. A sub-sample (N=1351) completed physical health measures (mean age=13.58 ± 2.13, range 10-18 years). Seventy five percent were aerobically fit, 77% had a normal BMI, 88% had a healthy waist circumference and 75% had a healthy BP. Those that met the ≥60 minutes of MVPA daily recommendation had the best health profile. Aerobically fit individuals engaged in less sedentary behaviour. This study supported an ecological approach to understanding PA in finding that a range of intra- and extra-individual factors predict MVPA. Males had higher PA enjoyment than females, enjoyment decreased with age and those in the upper socioeconomic status category reported higher enjoyment. Enjoyment had a significant impact on MVPA. Peer social support and club sport participation were the most salient predictors of PA enjoyment. Future interventions should adopt an ecological approach to increasing PA among males and females. Physical activity enjoyment should be facilitated by encouraging peer social support and club sport participation.