The medial collateral ligament rupture is the most common injury involving the knee joint ligaments. The ruptured medial collateral ligaments of 73 cases with clinical and surgical confirmations were radiologically analized. The results were obtained as follows : 1. The most risky age for tearing of the medial collateral ligament was third to fifth decades (50 cases of male and 23 of female). 2. The most common cause of the medial collateral ligament rupture was traffic accident (82.2%). 3. The mean distance of medial knee joint space was 7.9$pm$2.0 mm. on the normal side and 13.7$pm$4.2 mm on the affected side. 4. The mean degree of knee joint space was 10.1$pm$2.5 on the normal side and 14.7$pm$3.8 on the affected side. 5. The fibula was the bone fractured most frequently in association with the medial collateral ligament rupture (30.6%).