Many factors are thought to cause ankle ligament in juries. The purpose of this study was to examine injury risk factors prospectively and determine if an abnor mality in any one or a combination of factors identifies an individual, or an ankle, at risk for subsequent inver sion ankle injury. We examined 145 college-aged ath letes before the athletic season and measured gener alized joint laxity, anatomic foot and ankle alignment, ankle ligament stability, and isokinetic strength. These athletes were monitored throughout the season. Fifteen athletes incurred inversion ankle injuries. Statistical analyses were performed using both within-group (un injured versus injured groups) data and within-subject (injured versus uninjured ankles) data. No significant differences were found between the injured (N = 15) and uninjured (N = 130) groups in any of the param eters measured. However, the eversion-to-inversion strength ratio was significantly greater for the injured group compared with the uninjured group. Analysis of the within-subject data demonstrated that plantar flex ion strength and the ratio of dorsiflexion to plantar flex ion strength was significantly different for the injured ankle compared with the contralateral uninjured ankle. Individuals with a muscle strength imbalance as meas ured by an elevated eversion-to-inversion ratio exhib ited a higher incidence of inversion ankle sprains. Ankles with greater plantar flexion strength and a smaller dorsiflexion-to-plantar flexion ratio also had a higher incidence of inversion ankle sprains.