The frequency and preferred localisation of overt subchondral osteonecrosis in large joints have been studied in a roentgenological and clinical study. Among 619 patients (454 female, 165 male) a severe subchondral osteonecrosis was found 44 times on one or more (maximum 3) large joints of 30 patients. The hip and shoulder joints were most frequently attacked, while patients with an advanced stage or longer duration of the disease and those in the middle age groups showed this most often. Osteonecrosis did not necessarily correlate with the activity of the disease process and with the presence of a positive rheumatoid factor. Radiologically, osteolytic appearances are seen most often in the elbow and osteochondritis dissecans in the knee joint. In the hip and shoulder joint the appearances are those of reparative states with a distinct demarcation, more rarely a severe osteolysis also involving the adjacent skeletal parts, occasionally a diffuse irregular lytic osteoporosis and necrosis. The pathogenesis is discussed in detail.