A study was undertaken to evaluate the effect of a semi-rigid ankle orthosis (Sport-Stirrup) on the incidence of ankle sprains in soccer players during 1 playing season. Senior soccer players were divided into 2 groups: players with previous ankle sprains (N = 258) and players without such history (N = 246). The players in these groups were each randomly allocated to either a semi-rigid orthosis or a control group at the start of the playing season. All subsequent injuries during the season and the total number of playing hours were documented. There was a significant reduction in the incidence of ankle sprains (injuries/1000 playing hours) by ankles in the orthosis group with previous sprains (0.14) compared with the nonbraced group with previous sprains (0.86). The incidence of ankle sprains was significantly higher in the nonbraced group with previous sprains (0.86) compared with the nonbraced group without previous sprains (0.46). Thus, in this study, a semirigid orthosis significantly reduced the incidence of recurrent ankle sprains in soccer players with previous history of ankle sprains.