A prospective study of orthopaedic injuries to children (ages 6 to 17) was conducted for a calendar year in the controlled environment of a military post. Data were collected on the number of participants, the hours of participation, and the number of injuries for six supervised sports (football, soccer, basketball, baseball, swimming, and gymnastics). An injury index factor was derived by a formula: (number of injuries x 104) divided by [(number of participants) x (average number of hours of participation) × (number of weeks in the season of the sport)]. When the injury index factors were compared, the risk a participant has for sustaining an injury in football was twice as high (1.72) as its nearest competitors, basketball (0.88) and gymnastics (0.85). Soccer had an index factor of 0.29; baseball, 0.14; and swimming had a factor of zero. Eighty percent of all sports-related orthopaedic injuries involved the upper extrem ities. Lower extremity orthopaedic injuries occurred only in football and gymnastics. The evidence suggests that those persons concerned with reducing the number of injuries to the growing athlete in supervised sports should focus their attention on reducing the risk of injury to the upper extremities.