Recurrent anterior subluxation of the lateral tibial plateau is a common type of chronic knee instability resulting from trauma. It can be reproduced by the clinical test described and corrected by a surgical procedure called the sling and reef operation, in which a strip of iliotibial tract is used to create a sling and to reef the posterolateral capsule. From 1971 to 1978, eighty-four patients were operated on, of whom fifty had been evaluated at one to six and one-half years after operation. The results were: forty-one good, six fair, and three poor. The lesions found in the thirty-seven knees in which arthrotomy was performed included a tear of the anterior cruciate in every case, a tear of the medial meniscus in fifteen and of the lateral meniscus in eleven, a notch in the articular surface of the lateral femoral condyle in fifteen, and a lateral marginal tibial (Segond) fracture in three. No definite lateral capsular tears were visualized--only stretching comparable to that seen in recurrent dislocation of the shoulder.