The authors discuss lateral differences between heel bones during ultrasonic bone densitometry using the apparatus Achilles Lunar. While the mean values for the whole group are statistically insignificant (162 patients) in different parameters (SOS, BUA, stiffness) in one quarter of the patients the differences between the two extremities are greater than 9% which may be a source of errors when evaluating the state of the skeleton and when subsequently deciding on treatment.