The use of ultrasound for evaluation of the knee is increasing. Although it cannot replace magnetic resonance imaging (MRI), which has been the modality of choice in conjunction with plain radiographs, ultrasound does have certain advantages in knee diagnosis. For example, in South Africa the cost of an ultrasound examination is approximately 10% of the cost of an MRI scan. Ultrasound is a very cost-effective alternative for imaging of the knee, providing the indications, advantages, and limitations are understood. Probably the greatest advantage of ultrasound, however, is for the detailed evaluation of the soft tissues within and surrounding the knee. These include ligamentous, tendinous, fibrous, fatty, synovial, and neurovascular structures. These tissues can be assessed for size, continuity, anatomic orientation, and echogenecity; furthermore, they can be readily compared contralaterally. Evaluation of intra-articular elements such as the menisci, cruciate ligaments, and articular cartilage is limited mainly by inaccessibility, which results from the small acoustic windows obtainable in most patients. This liberally illustrated article reviews ultrasound of the knee, including anatomy, ultrasound technique, and pathologic findings.