PURPOSE: To evaluate the differential features of complete and partial-thickness tears of the anteriorcruciate ligament, as seen on magnetic resonance imaging(MRI). MATERIALS AND METHODS: We retrospectvely reviewedMR images of 36 patients with ACL injuries (complete tear 16, incomplete tear 20). In all cases, the presence ofan ACL tear was determined by arthroscopy or surgery. Primary and secondary signs of ACL injury and associatedinjuries were assessed. RESULTS: Ligamentous discontinuity of the ACL was observed in ten complete tears (63 %),but in only four (10%) of those that were partial (p=0.009). In addition, complete tears were more likely to showa low degree of ACL axis, less than 45 degree(11/16 : 2/20, p=0.001). There was, however, no statistically significantdifference between complete and partial tears with regard to signal intensity of ACL, PCL buckling or angle,anterior dis-placement of the tibia, uncovered meniscus sign, deep notch sign, empty notch sign, and associatedinjuries. CONCLUSION: Ligamentous discontinuity and the ACL axis are features which usefully differentiatebetween complete and partial tears of the ACL.