In order to know the causes of protrusio acetabuli and destruction of the femoral head in rheumatoid arthritis, the relationship between protrusio acetabuli, destruction of the femoral head and strength of bone were examined radiologically. Material consists of 24 hips in 14 cases, which were followed up for more than 6 months. Protrusio acetabuli had a tendency to occur in the cases which have high osteoblastic response in the femoral head and severe systemic osteoporosis. On the other hand, destruction of the femoral head was hardly observed among the cases which have normotrophic osteoblastic response in the femoral head and acetabulum, but it does not related to the osteoporosis. In conclusion, it was suggested that the development of changes of the hip joint in rheumatoid arthritis was related to the bone strength of the hip and systemic osteoporosis.