From a sample of 849 adolescents studied at age 15, 429 had been involved in 657 separate incidents, which resulted in 705 acute injuries requiring medical attention during their 14th and 15th years of life. The most common injuries were sprains, strains, fractures and lacerations, and the most common body site was the finger. The majority of injuries were of minor severity. Striking against an object or person was the most common incident resulting in injury, followed by being struck by an object or person, and overexertion or strenuous movement. Approximately half of the injuries were incurred during sport or a similar physical activity. Sporting injuries are examined in detail and preventive measures discussed.