The popliteal tendon has a significant attachment to the fibula, the popliteofibular ligament. The role of this ligament in knee stability has not been determined. In this study we used selective cutting techniques to measure the static contribution of the popliteal tendon attachments to the tibia and the popliteofibular ligament for stability of the knee. Sectioning of all the posterolateral structures except the popliteal tendon attachments to the tibia or the popliteofibular ligament resulted in increased primary posterior translation, varus rotation, external rotation, and coupled external rotation. Although statistically significant, these increases were small. Sectioning of all the posterolateral structures resulted in larger increases in primary posterior translation, varus rotation, external rotation, and coupled external rotation. Our data indicate that the popliteal tendon attachments to the tibia and the popliteofibular ligament are important in resisting posterior translation and varus and external rotation. If an isolated injury to the posterolateral structures occurs, anatomic reconstruction of the major ligaments that restrain posterior translation and varus and external rotation may provide the best functional result. Reconstruction for isolated posterolateral instability should include anatomic attachment of the popliteal tendon to the tibia and the popliteofibular ligament.