Objective: The aim of this study is to evaluate the influence of the tibial slope and the size of the inter condylar notch on rupture of the anterior cruciate ligament and to predict the athelets who more susceptible to ACL injuries. Background: The anterior cruciate ligament (ACL), which is located in the intercondylar notch of the femur, is one of the major stabilizing intra capsular ligaments in the knee joint. ACL is proximally attached to the postero-medial surface of the lateral femoral condyle and distally to the anterior part of the inter condylar eminence of the tibia. Injuries to the knee joint are common in athletes and the ACL is the most frequently ruptured ligament of the knee. The purpose of this prospective study is to establish a normal range for the notch width index and to correlate inter condylar notch size and anterior cruciate ligament injuries. The normal intercondylar notch ratio is 0.231 +\0.044. The inter condylar notch width index for men is larger than that for women. ACL injuries have statistically significant inter condylar notch stenosis. The posterior tibial slope (PTS) plays a very important role in the kinematics and biomechanics of the knee joint. Increased medial PTS has been reported to be associated with anterior cruciate ligament (ACL) injuries in teenagers and adult. Patient &Methods: We will follow about 50 cases complaining of knee pain and follow up them. We will divide them to two groups GROUP A; with ACL injuries GROUP B (controlled group); with intact ACL and we will measure the posterior tibial slope and notch index in both groups to compare the results in both groups. We will measure posterior tibial slope from lateral view of plain X ray and the notch index from coronal view of MRI. Patient Age: Adult > 15 years old Patient admitted to Al azhar university hospitals (El – Hussien and Sayed Galal Hospitals). Results: The group with ACL rupture had a statistically significantly increased PTS and a smaller NWI than controlled group. When a high PTS and / or a narrow NWI were defined as risk factors for ACL rupture, 80% of patient had at least one risk factor present, only 24% had both factors present. In both groups the PTS was negatively correlated to the NWI. PTS and NWI appear to be correlated to rupture of the ACL. From these results, either a steep PTS or a narrow NWI predisposes an individual to ACL injury. From these results, both PTS and NWI appear to be correlated with ACL rupture, When a high tibial slope (> 10.5) and /or a tighter notch (NWI< 0.22) were introduced as risk factors for ACL injury, 88% of the patients in the ruptured ACL group had one (52%) or two (36%) risk factors present, only 12% of (group 1) with ruptured ACL have normal values of posterior tibial slope and notch width index. Conclusion: It has been suggested that an increase posterior tibial slope (PTS) and a narrow notch width index (NWI) increase the risk of anterior cruciate ligament (ACL) injury. [Ahmed Abd-Elhamid Shamma, Tharwat Abd-Elghany Elsayed and Amr Ahmed Khattab. The Effect of Tibial Slope and Size of the Intercondylar Notch on Rupture of the Anterior Cruciate Ligament. Nat Sci 2016;14(12):254-260]. ISSN 1545-0740 (print); ISSN 2375-7167 (online). http://www.sciencepub.net/nature. 40. doi:10.7537/marsnsj141216.40.