During the past ten years the range of treatments available for patients with osteoporosis has increased greatly. A decade ago the only proven therapy was oestrogen, while today the choice includes bisphosphonates, selective oestrogen receptor modulators, calcitonin, calcium and vitamin D supplementation and, in the near future, parathyroid hormone. Clinical trials involving bone mineral density (BMD) scans of the spine and femur have had an important role in the evaluation of these new therapies. Supplementary information about treatments has been provided by BMD scans of the total body and distal radius as well as by measurements of biochemical markers of bone turnover in serum and urine. Most important of all, the efficacy of treatments has been verified in large trials powered to show reductions in fracture risk. In routine clinical use, BMD scanning has an important role in identifying individual patients with osteoporosis and helping to make decisions about their treatment. However, in contrast to the use of BMD scans in clinical trials, their value for monitoring response to therapy in individual patients is less certain because in many cases the increases in BMD are too small to reliably distinguish between true changes and measurement error. However, experience with well established therapies such as oestrogen and bisphosphonates suggests that these treatments have a beneficial effect on bone in the large majority of patients and individual monitoring of BMD is probably not necessary.