To investigate the correlations between traumatic injuries of the anterior cruciate ligament and other ligamentous, meniscal and bone traumatic injuries, a series of 193 patients with anterior cruciate ligament injuries studied with MRI between January 1992 and December 1994, was retrospectively reviewed. MR results were compared with arthroscopic and/or surgical findings in most (181) patients; in the remaining 12 patients, clinical follow-up was performed. We used two 0.5 superconductive MR units, with dedicated coils and T1-weighted spin-echo and T2*-weighted gradient-echo sequences on the axial, sagittal and coronal planes. Anterior cruciate ligament injuries were associated with other ligamentous, meniscal and bone injuries in 78% of patients. The patients were classified in 5 groups depending on biomechanics and the association of injuries: -group I: isolated injury of the anterior cruciate ligament (41 patients), most frequently caused by forced extension stress associated with "kissing contusions" of the anterior portion of the lateral femoral condyle and of the lateral tibial plateau; this type of injury is less frequently caused by forced flexion stress associated with avulsion fracture of the tibial eminence; -group II: associated injury of the anterior cruciate ligament and medial compartment (62 patients), caused by forced flexion-external rotation stress (abduction, valgism and external rotation). The classic association of this mechanism was the injury of the anterior cruciate ligament, medial collateral ligament and medial meniscus (O'Donoghue triad) (9 patients). Valgus stress and the pivot-shift phenomenon can impact the tibial and femoral articular surfaces, with consequent osteochondral contusion; -group III: associated injury of the anterior cruciate ligament and lateral compartment (26 patients), caused by forced flexion-internal rotation stress (adduction, varism and internal rotation). This mechanism can cause, as a typical bone lesion, Segond fractures; -group IV: associated injury of the anterior cruciate ligament, lateral and medial compartments observed in 52 patients with different associations of varus-valgus and rotatory stress; -group V: in 5 patients, anterior cruciate ligament injury was associated with traumatic injury of the posterior cruciate ligament; in this case, posterior displacement of the tibia and knee hyperextension were the most common mechanisms of injury. In conclusion, our results demonstrate that anterior cruciate ligament injuries due to traumatic sprains of the knee are rarely isolated (21%). Thus, it is important to know the biomechanics of knee trauma to read MR images in order to detect possibly associated injuries. The final goal is to assess the actual extent of the traumatic damage for best subsequent clinical-therapeutic management.