In the Swiss organization "Youth and Sports" all acute injuries that are attended to by a physician are registered by the Military Insurance, and data on the number of participants in 32 sports together with the time of exposure are collected by the organization. Per year there are close to 350,000 participants (age 14-20 years) during 13.2 million hours causing more than 5,000 injuries. In a descriptive study the data on the activities in "Youth and Sports" from 1987-1989 have been combined with the injuries which occurred during the same time period. The exposure to risk per 10,000 hours (incidence rate) has been calculated and is presented as a mean of the three years. Icehockey, handball and soccer had the highest incidences in males (8.6, 7.2, and 6.6) followed by wrestling, hiking and basketball (6.3, 3.6, and 3.5). In females the ranking order was handball, soccer and basketball (7.6, 6.7, and 4.9) succeeded by alpine skiing, volleyball and alpinism (3.9, 3.8, and 3.0). A comparison between males and females of the incidence rates in eleven analogous sports showed five significantly higher rates, four in female sports: basketball, alpine skiing, volleyball and apparatus gymnastics, and one in a male sport, hiking. The overall rate was significantly higher in males, but the higher risk was explained by the predominance of male soccer (56% of the injuries in males). After standardization for total exposure the results were even reversed and female sports had a higher overall risk.