Osteomalacia is characterized by defective mineralization and low bone mineral density (BMD). Clinical and biochemical improvements typically occur within a few weeks of starting treatment, though the bone mineral deficits may take longer to correct. We report a case series of 26 patients with frank osteomalacia (pseudo fractures on X-rays, elevated serum total alkaline phosphatase and parathyroid hormone, normal/low serum calcium and phosphorus, and low serum 25-hydroxy vitamin D) who were followed-up for changes in BMD during treatment using dual- energy X-ray absorptiometry (DXA). There were 23 patients with nutritional vitamin D deficiency, 2 with malabsorption syndrome, and 1 with renal tubular acidosis. All patients were treated with vitamin D and calcium; the 3 patients with associated disorders were treated accordingly. At baseline, there was low BMD at all sites tested. The rate of increase in vertebral and hip BMD was rapid in the initial few months, which subsequently slowed down. In contrast to the large increases in BMD at the femoral neck and lumbar spine, the radial BMD did not recover. At the time when most patients had marked clinical and biochemical improvement (2.8+/-1.4 mo), the vertebral and hip BMD, although improved from baseline, had not completely recovered. Bone loss at the forearm (cortical site) appears to be largely irreversible. Although the clinical correlates of these changes are presently unclear, BMD measurements are useful in assessing the initial severity of bone loss as well as the response to therapy.