Injury prevention is a priority in the field of sports medicine and in physical activity promotion, in particular for youth. Injuries can lead to long term handicaps and disengagement from physical activity. The follow up of young sportsmen in the canton of Geneva over the last 35 years has permitted to get an idea of the prevalence of injuries in young sportsmen and allows a comparison with the general population. It has also permitted to get an idea of the influence prevention has had on injuries.