Two male adolescents with direct trauma to the knee and haemarthrosis were followed up with MR imaging (MAI). No fractures were detected on plain films and both patients had extensive bone marrow lesions in MRI. The lesions were located within the metaphysis and the lateral tibial and femoral condyle respectively. In one patient MRI demonstrated additional soft tissue lesions of the femoral muscles. One patient had almost no clinical symptoms, while the other patient suffered from severe pain, inability to walk, and delayed recovery. The present report emphasizes the potential of MRI for the detection of occult injuries of bone and soft tissue, and calls for prospective studies of their clinical significance.