PURPOSE: To evaluate the characteristic MR findings in injury of the anterior cruciate ligament (ACL) with associated bony lesions. MATERIALS AND METHODS: We reviewed MR findings and the corresponding arthroscopic or operative results of 48 patients with ACL injuries, and evaluated ACL signal intensity and contour. In associated bony lesions, we determined the location of avulsion fracture and bony bruise. RESULTS: Cmplete ACL tears were seen in 27 cases, partial tears in 13, and avulsion injury in eight. Complete tears showed heterogeneously increased signal intensity with contour bulging in ten cases (37 %), and combined bony lesion in 14 (52 %). ACL with a thin continous low signal intensity band surrounding heterogeneously-increased signal intensity suggested partial tears, and was seen in three of 13 proven cases (23 %) of partial ACL tears ; combined bony lesion was seen in four such cases (31 %). There were eight cases of avulsion fracture ; the most frequent site was the anterolateral portion of the tibial spine (n=6). The most frequent sites of bony lesion were at the midportion of the lateral femoral condyle (n=6), and the posterior portion of the lateral tibial plateau (n=6) ; the next most frequent site was the anterior portion of the lateral tibial plateau (n=5). CONCLUSION: Tearing of the ACL was seen on MRI as ligament discontinuity, and heterogeneously increased signal intensity with ACL contour bulging. The most frequent sites of associated bony lesions were the midportion of the lateral femoral condyle, and the posterior portion of the lateral tibial plateau. In associated bony lesions, bony contusion suggested ACL tearing, but avulsion fracture suggested ligament avulsion injury without tear.