A useful method for the diagnosis of acute rupture of the lateral ligament of the ankle joint is presented. Twenty-three patients with ruptures of the lateral ligament of the ankle joint were treated surgically with suture of the lateral ligaments of the ankle. Accurate preoperative diagnosis with stress films and arthrography under local anesthesia of the ankle joint is imperative. No instances of infection or other complications were observed. All patients achieved a normal range of ankle function within three to six months. Radiograhs of the injured ankle in the forced inversion position following operation showed full stability of the ankle joint. In our opinion, all ankle injuries should be examined roentgenographically with forced inversion of the foot. Tilting of the talus of at least 10 degrees must be followed by arthrography of the ankle joint under local anesthesia. If there is leakage of contrast material along the peroneal tendon sheaths and around the joint cavity, the lateral ligament of the ankle must be sutured immediately in order to regain stability of the ankle joint.