A four year follow up trial of 109 cases of the Wagner type of prosthetic surface replacement has been undertaken. It has been found that this type of arthroplasty has been associated with a higher rate of loosening that the conventional total hip replacement. This loosening mainly affects the femoral component. The morphological changes which occured below the loosened femoral component did not show typical avascular necrosis due to implantation of the prosthesis. The changes seen were due to mechanical failure of the bone which resulted from previous structural weakness of the femoral head. Hence loosening of the implant occurred mainly in femoral heads which had cysts, partial necrosis or osteoporosis. Loosening of the implant was not definitely related to the position of the hip and occured in both the valgus as well as the biomechanically unfavourable varus position.