BACKGROUND: Some sports, for example basketball and soccer, have a very high incidence of ankle injuries, mainly sprains. Consequently, ankle sprains are one of the most commonly treated injuries in acute care. OBJECTIVES: To assess the effects of interventions used for the prevention of ankle ligament injuries or sprains in physically active individuals from adolescence to middle age. SEARCH STRATEGY: We searched the Cochrane Musculoskeletal Injuries Group's specialised register, MEDLINE, PubMed, EMBASE, CINAHL, the National Research Register and bibliographies of study reports. We also contacted colleagues and some trialists. The most recent search was conducted in July 2000. SELECTION CRITERIA: Randomised or quasi-randomised trials of interventions for the prevention of ankle sprains in physically active individuals from adolescence to middle age were included provided that ankle sprains were recorded. Interventions included use of modified footwear, external ankle supports, co-ordination training and health education. These could be applied as a supplement to treatment provided that prevention of re-injury was the primary objective. DATA COLLECTION AND ANALYSIS: At least two reviewers independently assessed methodological quality and extracted data. Wherever possible, results of outcome measures were pooled and sub-grouped by history of previous sprain. Relative risks (RR) and 95% confidence intervals (95% CI) are reported for individual and pooled data. MAIN RESULTS: In this review update, a further nine new trials were included. Overall, 14 randomised trials with data for 8279 participants were included. Twelve trials involved active, predominantly young, adults participating in organised, generally high-risk, activities. The other two trials involved injured patients who had been active in sports before their injury. The prophylactic interventions under test included the application of an external ankle support in the form of a semi-rigid orthosis (three trials), air-cast brace (one trial) or high top shoes (one trial); ankle disk training; taping; muscle stretching; boot inserts; health education programme and controlled rehabilitation. The main finding was a significant reduction in the number of ankle sprains in people allocated external ankle support (RR 0.53, 95% CI 0.40 to 0.69). This reduction was greater for those with a previous history of ankle sprain, but still possible for those without prior sprain. There was no apparent difference in the severity of ankle sprains or any change to the incidence of other leg injuries. The protective effect of 'high-top' shoes remains to be established. There was limited evidence for reduction in ankle sprain for those with previous ankle sprains who did ankle disk training exercises. Various problems with data reporting limited the interpretation of the results for many of the other interventions. REVIEWER'S CONCLUSIONS: This review provides good evidence for the beneficial effect of ankle supports in the form of semi-rigid orthoses or air-cast braces to prevent ankle sprains during high-risk sporting activities (e.g. soccer, basketball). Participants with a history of previous sprain can be advised that wearing such supports may reduce the risk of incurring a future sprain. However, any potential prophylactic effect should be balanced against the baseline risk of the activity, the supply and cost of the particular device, and for some, the possible or perceived loss of performance. Further research is indicated principally to investigate other prophylactic interventions, their cost-effectiveness and general applicability.