The posterior cruciate ligament has been considered the basic stabilizer which performs important functions because of its location and orientation within the knee joint. Therefore, failure to recognize or to repair its tear results in a poorly functioning knee. An isolated injury to the posterior cruciate ligament is believed to be unconmon and is seen most commonly in association with other ligamentous injury and dislocation of the knee joint. But recently its injuries are of frequent occurrence because of increasing traffic accident and sports activities as football, soccer, and skiing. The authors experienced 12 cases of isolated posterior cruciate ligament injury from March, 1978 to February, 1982 at the Department of Orthopaedic Surgery, Capital Arrned Forces General Hospital and the results were as follows: 1. The most common cause of injury was passenger traffic accident (5 cases) and followed by soccer (4 cases), football (2 cases), and skiing (1 case). 2. There were 3 causative mechanisms by which the posterior cruciate ligament was injured; anteroposterior force on the front of the knee joint (5 cases), hyperextension of the knee joint (4 cases), and posteriorly directed rotatory force (3 cases). 3. Tears of the posterior cruciate ligament occured at its tibial attachment (5 cases), with avulsion of a bone fragment at its tibial attachment (3 cases), at its femoral attachment (2 cases), and its mid-portion (1 case). 4. The major findings in this injury included giving-way or instability on walking, abrasion or contusion over the anterior proximal tibial surface, presence of a posterior drawer sign, sagging of the tibia, bloody effusion, and X-ray evidence of avulsion fracture. 5. One case was treated conservatively and 11 cases surgically using screw fixation and direct or pull through suture through a posterior S-shaped incision (5 cases), medial parapatellar and posterior S-shaped incision (3 cases), and medial hockey-stick incision (3 cases) and were immobilized in a long leg cast with 30 to 45 degrees of the knee flexion for 6 to 7 weeks. 6. The results evaluated by Apleys method were excellent in 8 cases; good in 2 cases, and fair in 2 cases.