Previous recommendations for adolescents have stated that sexually immature athletes may have a higher potential for injury when competing with their more sexually mature peers. However, studies document a higher injury rate among adolescent athletes with increasing age. This study was designed to see whether a relationship exists between sexual maturity based on Tanner stage and the incidence of adolescent injuries in a collision sport where the injury rates are highest. Three hundred and forty junior high school football athletes, ages 11-15, were observed prospectively for injury over two consecutive football seasons. Tanner staging of all of these athletes was performed at the preparticipation physical exam before the start of each season. Fifty-five injuries were noted for this time period. The overall injury rate was 16%. A direct correlation was observed between higher Tanner stages and increased injury rates. Adolescent athletes who have recently experienced sexual maturation may be at higher risk of injury in contact sports.