MR imaging has surpassed all other imaging modalities to become the "gold standard" for imaging evaluation of ACL injury. The accuracy and sensitivity of MR imaging for evaluation of ACL tears is excellent when correlated with clinical tests and arthroscopic findings, and is improved in equivocal cases with assessment of secondary signs for ACL tear. The MR imaging assessment of partial and chronic ACL tears is less accurate but is clinically useful. MR imaging provides information about associated injuries prior to surgery. Radiologic diagnostic methods for the assessment of ACL tears on MR images are well established; recent techniques such as dedicated cartilage imaging offer new information of use to clinicians about the sequelae of ACL injuries.