A new radiologic classification of juvenile chronic arthritis (JCA) of the knee joint is presented. Osteoporosis, epiphyseal enlargement, erosions, subchondral cyst formation and deformity of the joint surfaces are expressed in terms of a score. No attention is paid to the joint space or soft tissues. Thirty knee joints in 15 patients with JCA were evaluated according to the radiologic classification. There was a good correlation between the radiologic score and the clinical findings. The inter- and intraobserver variation was low. The classification system is proposed as a valuable tool for measuring the degree of knee joint destruction in evaluation of the natural course or results of treatment in JCA.