To clarify changes in bone mass around a femoral prosthesis, periprosthetic bone mineral density (BMD) was measured by dual energy X-ray absorptiometry (DXA) in 60 patients after unilateral cementless hip arthroplasty. Changes in BMD were evaluated by cross-sectional analysis in all patients and by longitudinal analysis in 26 patients who were available for measurement from 1month to 2years after surgery. The mean reproducibility of BMD measurements was within 1.74% in vivo. Periprosthetic BMD began to decrease early after surgery, and although it recovered temporarily within 1year, it did not return to the level of the 1st month even after 2years. BMD was reduced by 30.4% in the whole periprosthetic region compared with the contralateral untreated femora 4–7years after surgery. The reduction in BMD was remarkable around the proximal part of the stem, especially in zone 7 (44.7 % reduction 4–7years after surgery). Significant positive correlations were observed between the low level of the preoperative cortical remodelling index and the reduction in BMD and between the preoperative femoral BMD and the reduction in BMD, indicating that the postoperative bone loss was greater in patients who preoperatively showed quantitative and qualitative deterioration of the femur.