We compared broadband ultrasonic attenuation (BUA) values of right with left os calcis in 65 women. All subjects were right handed, and they were divided into two groups: Group 1 consisted of 32 normal volunteers and Group 2 of 33 osteoporotic subjects. Both groups had mean absolute differences in BUA between the two os calces greater than the coefficient of variation (p < 0.001). This difference is not related to stated handedness of the individuals. Osteoporosis affects both os calces similarly. BUA measurements should always be performed in the same site in longitudinal studies, otherwise false comparisons will result.