The incidence of injuries among youth soccer players (under age 16) participating in indoor soccer was 4.5 times that of youth players in outdoor soccer when calculated per 100 hours of team play, and 6.1 times greater when calculated per 100 hours of player game participation. Injuries were few among players under age 10 in either game, and the number of injuries increased with age in the older players. Medical assistance was required for 6.5% of the injuries among outdoor players and for 24.3% among indoor players. Overall, 66.6% of the injuries were the result of physical contact between players. No relationship was observed between the risk of injury and playing position, conduct of warm-up exercises, or the team having a licensed coach.