Reduced bone mass is one of the main risk factors for fracture. An individual classification of future fracture risk can be made by relating bone mass to age- and sex-specific reference values. Since both bone mass and fracture incidence seem to be different in different populations, population-specific reference values should be studied before applying the reference values should by the manufacturers of the various types of measuring equipment. Using Lunar DPX-1, we measured bone mineral density (BMD) of the lumbar spine, femoral neck and total body in 225 women and 160 men in the age group 20-80 years, all of them from Oslo. The values were higher for men than for women. In the women the annual loss of bone increased after the age of 50 years in the lumbar spine and total skeleton, but the menopause appeared to have no effect for the femoral neck. Although the age- and sex-specific BMD differed very little from the reference values reported from Sweden and Finland, small differences in mean values and standard deviation between reference materials could create important differences in individual risk calculations if T-scores (deviation from mean value of premenopausal women calculated as standard deviation units) are used.