Pigmented Villonodular Synovitis is a kind of benign inflammatory lesion involving synovial membrane. characterized by yellowish or yellowgraysh colored villous nodules of synovial membrane, formed by accumulation of cholesterol and hemosiderin and numerous clefting of synovial membrane. This lesion was first described by Simon(1865)as Xanthoma of Synovia, and thereafter various names were given by many authors, according to its characteristics of pathological fetures. In 1941, Jaffe named this lesion Pigmented Villonodular Synovitis, which is now generally accepted. Still the direct cause of this lesion is not clearly known, but chronic stimulation to synovia is generally accepted as a criminal etiological factor. Actually, Young and Hudacek produced this lesion in animal experiments by chronic stimulations. but Jaffe failed. In this paper, we report three cases of Pigemented Villonodular Synovitis. which were experienced in our Department. One of the three cases showed recurrence in five years after the first reatction of this lesion.