A prompt, accurate diagnosis is essential in the management of acute ligamentous injury of the kriee. With the advent of MRI, the reported accuracy of diagnosis of ACL rupture is as high as 95%. Most MRI studies on ACL injury, however, could not differentiate partial from complete ACL ruptures accurately. It is important to differentiate partial from complete rupture. Because this distinction could be influence the patient management and prognosis. The purpose of this study is to assess the utility of indirect MRI signs for detecting tears and differentiating partial from complete tears of ACL. The present study included 40 patients, who were suspicious ACL injury in MRI finding and underwent arthroscopic examination of knee within one month after injury. At arthroscopy, there were 1 patient of normal, 10 partial and 29 complete ACL ruptures. The radiologist who did not know the arthroscopic findings have reviewed retrospectively and noted indirect MRI signs; ACL angle, PCL index, bone bruise, popliteus muscle injury, posterior displacement of lateral meniscus. Indirect signs in MRI showed significantly improve the detection of ACL rupture from ACL intact knees and help to distinguish partial from complete tear. Especially, among indirect signs in MRI, we consider that the displacement of posterior horn of lateral meniscus(more than 2.0mm) or popliteus muscle injury are indicative of complete ACL rupture.