Ankle sprains are often complicated by functional instability and repeated sprains. Rehabilitation with wobble boards in patients with functional instability has been tested, and significant improvement has been found compared to no training. The aim of this study was to investigate whether the number of patients with residual symptoms following ankle sprains could be reduced by training on a wobble board during 12-week recovery period. In addition, the influence of training in the time course reduction of edema was investigated. We performed a prospective study including 61 patients, all active in sports for more than 2 hours a week with primary ankle sprains. The effect of a 12-week training program with wobble board was compared with no training. Forty-eight patients completed the study. In the follow-up period (mean X = 230 days), we found significantly fewer recurrent sprains, and significantly fewer patients in the training group had functional instability of the ankle compared with the no training group. There were no differences in the two groups in the time which elapsed before patients were painless at walking, during running, or at sports. Volumetric measurements revealed no difference in the speed of reduction of hematoma and edema of the ankle and foot between the two groups. We conclude that training on a wobble board early after primary stage 2 ankle sprains is effective in reducing residual symptoms following this lesion and that training does not seem to affect the time course reduction in edema.