A variety of benign tumors of the synovium must be considered in the differential diagnosis of knee-joint dysfunction. This paper summarizes the data on the incidence of ninety-five such tumors and reports six representative cases.

Although synovial chondromatosis and sometimes pigmented villonodular synovitis may produce a similar picture, one should suspect that the synovium of the knee may be involved by tumor when swelling, pain, and, sometimes, limitation of motion or catching occur. If there is no history of a specific trauma and, as is usually the case, the roentgenographic appearance of the knee is normal, one's suspicion should be enhanced.

At the time of arthrotomy the knee joint should be thoroughly inspected, since small synovial tumors may be obscure and difficult to find. Every attempt at localization should be made preoperatively in order to help lead one to the proper area of the knee during the surgical exploration.

Arthrography was not used in any patients of this series. It may be of help, but we believe that a careful history and examination, followed by thorough exploration, provide an accurate method of diagnosing these tumors. Treatment depends on the type of tumor and the extent of its involvement of the synovium.