OBJECTIVE: To review the prospective studies of ankle-ligament-injury risk factors. DATA SOURCES: We searched MEDLINE from 1978 to 2001 using the terms ankle, ligament, injury, risk factor, and epidemiology. DATA SYNTHESIS: The results included many studies on the treatment and prevention of ankle injuries. There were, however, very few prospective studies focusing on identifying the risk factors that predispose an athlete to ankle-ligament trauma. CONCLUSIONS/RECOMMENDATIONS: There is some agreement among authors with regard to the risk factors for ankle-ligament injury; however, considerable controversy remains. Although female athletes are at significantly greater risk of suffering a serious knee sprain, such as disruption of the anterior cruciate ligament, this does not appear to be the case for ankle-ligament sprains. Therefore, sex does not appear to be a risk factor for suffering an ankle-ligament sprain. Athletes who have suffered a previous sprain have a decreased risk of reinjury if a brace is worn, and the consensus is that generalized joint laxity and anatomical foot type are not risk factors for ankle sprains. However, the literature is divided with regard to whether or not height, weight, limb dominance, ankle-joint laxity, anatomical alignment, muscle strength, muscle-reaction time, and postural sway are risk factors for ankle sprains. Future research is needed on this topic to develop a consensus on all ankle-injury risk factors. This will allow future intervention studies to be designed that will reduce the incidence and severity of this common injury.