We included 23 patients operated with total hip prosthesis (THP). They were measured with DXA at 1, 5 and 14 days, 3 and 12 months after the operation. Results were given in percent (+/-SD) for each Gruen zone. There were no changes in bone density between the first 3 measurements. In all zones, except zone 1, the lowest BMD was measured after 3 months. We concluded that DXA measurements done within 14 days after the operation can be used as reference measurements for later follow ups.