A 60-year-old Caucasian woman with a 1-year history of pain at the ribs, spine, and pelvis consulted at our Institute in March 1999. She brought a bone densitometry performed using a Lunar DPX densitometer that showed bone mineral density (BMD) measurements in the osteoporotic range at both the lumbar spine and the femoral neck. As a child she had had bowed legs and had been treated with ultraviolet radiation. Results of the laboratory test performed at our institute showed normal total serum calcium, repeated low serum P levels, and a low renal phosphate threshold with elevated total and bone fraction of alkaline phosphatase with normal intact parathyroid hormone (PTH). A diagnosis of hypophosphatemic osteomalacia due to renal phosphate leak was made. She began treatment with neutral sodium phosphate at 1.5 g/day and calcitriol 0.5 microg/day. Her serum P levels normalized, and there was a progressive decrease in alkaline phosphatase levels. The densitometry showed a very rapid increase in BMD values with normalization at the lumbar spine after 10 months of treatment. This case shows the importance of bone densitometry in the follow-up of patients with suspected osteomalacia.