Despite the increasing use of MRI in knee disorders, ultrasonography remains the first choice examination technique in para-articular disease. The technique is fast, cheap, easily accessible and usable in the acutely injured patient. The choice of equipment, positioning of the patient and some characteristics of normal anatomy are described. The routine applications of ultrasonography include different types of tendon disease, trauma of the collateral ligaments, bursal pathology, joint effusions and synovitis, evaluation of the popliteal fossa and para-articular swellings. Other possible applications, somewhat more depending on the examiner's experience, are meniscal disease, trauma to the cruciate ligaments and evaluation of the articular cartilage and synovial plicae.