A partial tear of the anterior cruciate ligament is a frequent pattern of ACL injury, observed in 10 to 27% of isolated ACL lesions. There are three reasons to preserve these remnants: biomechanical, vascular and proprioceptive advantages for the patient. Good quality fibers work as graft protection during the healing process. Periligamentous and endoligamentous vessels present into the native ACL tissue may enhance the vascularization of the ACL augmentation. Mechanoreceptors still remaining in the residual ACL fibers may have proprioceptive function. Definition is controversial, based on anatomy, on clinical examination, on instrumental laxity assessment or on MRI findings. Continuous remnant ACL fibers bridging the femur and tibia, from native femoral ACL footprint to native tibial ACL footprint seem to be a good definition. Diagnostic is suspected by accumulation of arguments brought by a thorough clinical examination, precise MRI analysis and examination under anesthesia. But the final diagnostic needs an arthroscopic evaluation to confirm the presence of fibers in good position and to validate its good mechanical properties. The treatment of ACL partial tear is a demanding surgery; difficulties to visualize the graft insertion site, especially on the femoral side, require a perfect knowledge of the normal anatomy of the native ACL footprint. Adapted portals, perfect controls of the tunnel drilling process, intercondylar notch space management are the keys of success. The pivot shift test under anesthesia, a hard stop Lachman test, MRI findings, level and type of sport, arthroscopic aspects of the remnants and its mechanical properties, allow the surgeon decide between non operative treatment, ACL augmentation or standard ACL reconstruction.