Twenty-nine cases of pigmented villonodular synovitis (PVS) of the knee in 27 patients were reviewed to determine characteristic roentgenographic findings. All cases met strict histologic criteria for diagnosis. Four cases were localized PVS (LPVS), and 25 cases were diffuse PVS (DPVS). Roentgenographic findings were largely in the soft tissues. Cystic invasion of bone or degenerative changes were rare, although present in some cases. When present in DPVS, these changes were most pronounced in the patellofemoral articular surface. In the cases of DPVS, large posterior tumefactions did not correlate with extraarticular extension. Clinical behavior of PVS was governed more by anatomic site and form of disease than by the severity of histologic or roentgenographic findings.