Sports injuries are one of the most common injuries in modern western societies. Treating sports injuries is often difficult, expensive and time consuming, and thus, preventive strategies and activities are justified on medical as well as economic grounds.A successful injury surveillance and prevention requires valid pre- and post-intervention data on the extent of the problem. The aetiology, risk factors and exact mechanisms of injuries need to be identified before initiating a measure or programme for preventing sports injuries, and measurement of the outcome (injury) must include a standardised definition of the injury and its severity, as well as a systematic method of collecting the information. Valid and reliable measurement of the exposure includes exact information about the population at risk and exposure time. The true efficacy of a preventive measure or programme can be best evaluated through a well-planned randomised trial.Until now, 16 randomised, controlled trials (RCT) have been published on prevention of sports injuries. According to these RCT, the general injury rate can be reduced by a multifactorial injury prevention programme in soccer (relative risk 0.25, p < 0.001, in the intervention group), or by ankle disk training, combined with a thorough warm-up, in European team handball [odds ratio 0.17; 95% confidence interval (CI) 0.09 to 0.32, p < 0.01]. Ankle sprains can be prevented by ankle supports (i.e. semirigid orthoses or air-cast braces) in high-risk sporting activities, such as soccer and basketball (Peto odds ratio 0.49; 95% CI 0.37 to 0.66), and stress fractures of the lower limb by the use of shock-absorbing insoles in footwear (Peto odds ratio 0.47; 95% CI 0.30 to 0.76).In future studies, it is extremely important for researches to seek consultation with epidemiologists and statisticians to be certain that the study hypothesis is appropriate and that the methodology can lead to reliable and valid information. Further well-designed randomised studies are needed on preventive actions and devices that are in common use, such as preseason medical screenings, warming up, proprioceptive training, stretching, muscle strengthening, taping, protective equipment, rehabilitation programmes and education interventions (such as increasing general injury awareness among a team). The effect of a planned rule change on the injury risk in a particular sport could be tested via a RCT before execution of the change. The most urgent needs are in commonly practised or high-risk sports, such as soccer, American football, rugby, ice hockey, European team handball, karate, floorball, basketball, downhill skiing and motor sports.