In the international scientific literature, MRI is reported to identify anterior cruciate ligament tears with high diagnostic accuracy (80-95%). In this prospective analysis, 274 MR examinations of the knee were performed to develop a method to measure even slight sagittal dislocation of the tibia relative to the femur as a predictor of an anterior cruciate ligament tear. Ninety-eight patients presented a healthy anterior cruciate ligament and were therefore considered as a control group. In 92 cases, a complete tear of the anterior cruciate ligament was observed; in 78 cases the injury was partial and in 6 cases the posterior cruciate ligament was injured. Our results had arthroscopic, surgical or clinical confirmation in all cases. The measurements were carried out on an MR image of the sagittal midplane of the knee and served to calculate a ratio (Y/X) which quantifies the degree of possible tibial dislocation. The results served to establish a range for classifying the status of the anterior cruciate ligament in three categories: 1) undamaged ligaments (Y/X < 3), 2) interstitial injury (2.2 < Y/X < 3) and 3) complete tear (Y/X < 2.2). This simple and easy-to-apply method should be considered complementary to conventional MR examinations. The results are extremely useful in the analysis of acute injuries where other radiologic and symptomatologic techniques are not completely reliable.