To examine (1) sport participation and (2) sport injury in adolescents. This was a retrospective survey design. In total, 2873 adolescents were recruited from a random sample of classes from 24 Calgary and area high schools. Each subject completed an in-class questionnaire in March 2004. Overall and sport-specific participation rates (number of sport participants/number of students completing survey). Overall and sport-specific injury rates (number of injuries/number of participants). In the previous 1 year, 94% of students participated in sport. The top 5 sports by participation for males were basketball, hockey, football, snowboarding, and soccer, and for females, basketball, dance, volleyball, snowboarding, and soccer. The injury rate including only injuries requiring medical attention was 40.2 injuries/100 adolescents/y (95% CI, 38.4-42.1), presenting to a hospital emergency department was 8.1 injuries/100 adolescents/y (95% CI, 7.1-9.2), resulting in time loss from sport was 49.9 injuries/100 adolescents/y (95% CI, 48-51.8), and resulting in loss of consciousness was 9.3 injuries/100 adolescents/y (95% CI, 8.3-10.5). The greatest proportion of injuries occurred in basketball, hockey, soccer, and snowboarding. The top 5 body parts injured were the ankle, knee, head, back, and wrist. The top 5 injury types were sprain, contusion, concussion, fracture, and muscle strain. A previous injury was associated with 49% of the injuries and direct contact with 45% of injuries. Rates of participation in sport and sport injury are high in adolescents. Future research should focus on prevention strategies in sports with high participation and injury rates to maximize population health impact.