Notch stenosis had been thought to be related with anterior cruciate ligament (ACL) injury. The purpose of this study is to evaluate the possible relationship between notch stenosis and ACL injury. We measured the notch seen on the axial section in MRI at popliteal groove. We have retrospectively analyzed 116 cases of knee MRI. All cases were divided into three groups ; Group I were fifty six normal knee. Group II were thirty knee with contact ACL injuries. Group III were thirty knee with non contact ACL injuries. The result were as follows; 1. Statistically significant difference was found in the notch width index (NWI) between group I and group III but no significant differences was found in the NWI between group I and group II. 2. Statistically significant correlation to non-contact ACL injuries was found in the NWI at both anterior and posterior outlet of the notch. 3. An unique shape of the notch was found in the majority of group III.There seemed to be an obvious relationship between notch stenosis and non-contact ACL injuries.