Dual energy X-ray absorptiometry (DXA) measurements of bone mineral density (BMD) in the lumbar spine and femoral neck have been performed in 1000 consecutive women aged between 40 and 60 years referred for screening for osteopenia. A detailed history was taken from each woman that included relevant lifestyle parameters and known risk factors for osteoporosis. After exclusions, e.g. because of fractures, corticosteroid or prolonged HRT use, 627 women (mean age 53 years) were considered suitable for further analysis. The mean BMD in the lumbar spine (L1–L4) was 0.946 g/cm2 and in the femoral neck was 0.767 g/cm2. Significant correlations were found between BMD and years after the menopause and weight (range r = 0.20–0.24). However, these parameters are not reliable enough predictors of BMD to be of value in clinical practice. If osteopenia is to be the basis for initiating prophylactic measures against bone loss, then a threshold BMD must be chosen below which treatment will be advised. Since the correlation coefficient between spinal and femoral neck BMD measurements was only 0.64, assessment of any individual requires consideration of both sites. There is as yet no consensus as to the number of women who may require to be treated and we have provided BMD values that identify a range of population sizes (the lowest 20, 30, 40 and 50 percentiles). It should be noted that there was a 16% loss of BMD in the spine and 14% in the femoral neck during the first 5 years after the menopause. If prophylactic treatment for bone loss is to be used, there is an advantage in initiating treatment early after the menopause to maintain bone mass at the highest possible level.