Knee joint radiographs from 45 patients with articular chondrocalcinosis (CC), 23 with osteoarthrosis (OA) and 19 with rheumatoid arthritis (RA) were compared. The incidence of conventional radiographic features of osteoarthrosis, osteophytes, joint space narrowing subchondral cysts, subchondral sclerosis, and varus or valgus deformity was equal in CC and OA joints. But distinctive changes in the patello-femoral area were found in half of the CC joints. Twenty knees evidenced flattening of the anterior parts of the femoral condyles, 13 showed a large erosion on the anterior surface of the femoral shaft just above the condyles and in 10 cases these changes were coincidental. OA and RA joints never showed femoral shaft erosion, but 2 OA and 1 RA joint showed condylar flattening. The 23 CC joints with erosion or flattening showed less femorotibial osteoarthrosis than the 22 CC joints without these changes.