39 patients with osteoarthritis of the hip were randomized to receive either a resurfacing hip replacement (RHR) or a total hip replacement (THR). Bone mineral density (BMD) of the acetabulum, femoral neck, and proximal femur were measured throughout the course of the study in order to determine which hip replacement method preserves the bone mineral density of the acetabular side. By the end of the 2 year study period, it was found that resurfaced hip replacements maintained femoral neck and proximal femoral bone mineral density better than total hip replacements, but bone mineral density was maintained equally well by both forms of hip replacement on the acetabular side.