Clinical evaluation of posterolateral complex injuries of the knee can be difficult. To determine if magnetic resonance imaging can assist in decision-making in the treatment of posterolateral complex injuries, six consecutive patients with acute posterolateral knee trauma were imaged preoperatively with standard magnetic resonance imaging sequences. Magnetic resonance imaging findings were then correlated with results of examination under anesthesia or open lateral reconstruction. There were five complete lateral complex injuries (grade III) and one partial tear. Magnetic resonance imaging was able to accurately depict the extent of injury preoperatively in each case. All patients had concomitant anterior cruciate ligament tears. There was one partial posterior cruciate ligament tear. Visualization of the arcuate complex, biceps femoris tendon, lateral capsule, iliotibial band, popliteal tendon, and lateral collateral ligament was possible. A characteristic bone contusion on the anteromedial femoral condyle was present in all patients with complete posterolateral disruptions. Lateral complex injuries of the knee can be very accurately demonstrated on magnetic resonance imaging, and this imaging technique can be used to clarify the exact nature of the injury to allow better surgical planning.