PURPOSE: To evaluate the passive subluxation of the tibia on MR' images in patient with both anterior cruciate ligament (ACL) and medial collateral ligament (MCL) tears and to demonstrate the usefulness of its measurement. MATERIALS & METHODS: The authors performed a retrospective study of 123 knees with tears of both ACL (complete, n=70, partial, n=53) and MCL (complete, n=10, partial, n=113). ACL tears were documented at arthroscopy and MCL tears were interpreted by abnormal MR findings. One hundred normal knees were also studied for comparison. Using new internal landmarks, anterior subluxation was measured on an intercondylar sagittal image and lateral subluxation was measured on a mid-coronal image. RESULTS: Anterior subluxation of 3 mm or more was seen in 45/123(37%) abnormal knees, lateral subluxation of 3 mm or more in 20/123 (16%), and anterolateral subluxation in 15/123 (12%). Anterior subluxation of 5mm or more was seen in 25/70 (36%) complete ACL tears, and no knees with partial ACL tears showed anterior subluxation of 5 mm or more. CONCLUSION: Static anterolateral subluxation of the tibia occurs in knees with combined ACL and MCL tears, as measured on routine MR imaging. These measurements may help confirm the presence of ligament injuries and differentiate complete from partial ACLtear.