The traditional assessment of fracture healing by manipulation and viewing of radiographs is subjective and qualitative. Dual energy x-ray absorptiometry by contrast provides an accurate, precise, and minimally invasive quantitative measure of bone mineral density, a property that shows strong correlations with various mechanical properties of bone. Fourteen patients with unilateral tibial shaft fractures stabilized by external fixation were monitored with dual energy x-ray absorptiometry at monthly intervals after fracture. Fractured and contralateral unfractured bones (controls) were scanned on each occasion. Changes in mineralization with time over the whole length of the fractured bone could be seen. The most pronounced effects were visible in the area of the fracture, with a minimum recorded fracture site bone mineral density of 38 +/- 13% of contralateral values, but often more long term alterations in bone mineral density affected regions at some distance from this zone. Significantly, in four patients who had scans 5 or more months after fracture, the mineralization at the fracture site had returned to control levels, whereas bone mineral density in a region proximal to the fracture showed evidence of persisting posttraumatic osteoporosis.