Multiplanar spin-echo magnetic resonance imaging was performed on 54 patients with acute complete anterior cruciate ligament tears. Imaging was done within 45 days of index anterior cruciate ligament injury. Spin-echo T1- and T2-weighted images were used to determine the lesion morphology and location. Only the T2-weighted sagittal images were used for the incidence assessment; T2-weighted spin-echo imaging reflects free water shifts and best indicates the acute edema and inflammatory changes from injury. Eighty-three percent (45 of 54) of the knees had an osseous contusion directly over the lateral femoral condyle terminal sulcus. The lesion was highly variable in size and imaging intensity; however, the most intense signal was always contiguous with the subchondral plate. Posterolateral joint injury was seen in 96% (43 of 45) of the knees that had a terminal sulcus osseous lesion determined by magnetic resonance imaging. This posterolateral lesion involves a spectrum of injury, including both soft tissue (popliteus-arcuate capsuloligamentous complex) and hard tissue (posterolateral tibial plateau) injuries. The consistent location of the osseous and soft tissue injuries underscores a necessary similar mechanism of injury associated with these acute anterior cruciate ligament tears. Based on these characteristic findings, several proposed mechanisms of injury are discussed.