Purpose : To evaluate the sensitivity of MR imaging in determining tear sites and degrees in acute anteriorcruciate ligament tear. Materials and Methods : MR imagings were undertaken in 19 patients who had trauma on theirknee joints. All imaging studies were performed within 2 weeks after trauma and compared with operative findings.The degrees of ligament tear were divided into complete and incomplete, and sites of tears were divided intosuperior, middle and inferior portions. MR findings were compared with operative findings. Results : There were 14cases of complete ligament tear and 5 cases of partial ligament tear. We could diagnose correctly in all 14 caseswith complete tear and in 3 of 5 cases with partial tear. The tear sites were correctly predicted in 10 of 14cases with complete tear(71%) and 1 of 5 cases with partial tear(20%). In complete tears, MR findings weretransversely or obliquely coursed band-like high signal intensity within the ACL or abrupt switch over to asindistinct signal intensity. In partial tears, the tear sites could not be evaluated mostly and the tears appearedas linear low signal intensity lesions in posterolateral bundles of ACL. Conclusions : MR revealed highersensitivity in determining the degree and sites of ACL tear in complete tear as compared with partial tear.