A total of 621 women, aged 30-80 years, who were grouped according to having single (group 1) or duplicate measurements of their both calcanei with quantitative ultrasound (QUS) on the same day (group 2) or on a different day than the first measurement (group 3) were evaluated for differences between the right and left foot. Despite similar mean values of QUS indices on both sides, individual percentage differences were found varying from 7.3 to 9.5% in the quantitative ultrasound index (QUI), from 11.1 to 12.5% in broadband ultrasound attenuation (BUA), from 0.62 to 0.86% in speed of sound (SOS) and from 8.9 to 10.9% in estimated heel bone mineral density as measured using the Sahara Clinical Bone Sonometer in three groups of subjects. The percentage of subjects with a proportional difference exceeding the coefficient of variation of duplicate measurements of the same heel was the highest for BUA, varying from 63 to 76.7%, and ranged between 43.1 and 76.7% in other QUS indices. We conclude that there is a real inter-individual difference between the right and left foot in QUS parameters, whether measured once or twice or on different occasions. We recommend measuring both sides when using QUS to avoid misleading implications regarding a subject's bone status.