The effects of adipose tissue on the absorptiometric measurement of bone mineral mass has been estimated mathematically. The error caused by adipose tissue in the bone has been determined from a formula derived from the exponential equations describing the attenuation of mono-energetic x-rays. At the radius site, 6 cm from the proximal end, the accuracy error ranged from 1.5 to 5.5% at 27 kev, and from 2.5 to 8.5% at 60 kev. This accuracy error can be affected by calibration techniques. The imprecision due to adipose tissue in the bone was 1.2% at 27 kev, and 1.8% at 60 kev, and is independent of calibration techniques.