Posterolateral knee injuries may present as isolated injuries, an associated injuries with the ACL or PCL or part of the multiple-ligament knee injuries which determined by clinical tests and addressed using radiography, MRI or arthroscopy. Thirteen patients included in this study with a primary diagnosis of grade III posterolateral knee instability, three were acute combined injuries underwent repair, three were chronic combined and seven were chronic isolated injuries. Nine of the chronic cases underwent reconstruction and one isolated chronic case underwent high tibial osteotomy only. Four months postoperatively after rehabilitation protocole 10 patients were rated normal and nearly normal and complications include residual varus laxity, common peroneal injury and postoperative infection. Injuries to the posterolateral corner of the knee can lead to chronic instability if missed or inappropriately managed. Also can lead to increased stress on associated cruciate reconstructions.