en Endocrinology Endocrinology Original Research Original Research <p> <strong> Background: </strong>Dual-energy X-ray Absorptiometry (DXA) is considered the gold standard for non-invasive measurement of bone mass. T-scores and Z-scores are used to present the results of bone mass. The present study was designed to evaluate the discordance between T-scores and Z-scores calculated at a same level and its relation with age, gender and body mass index (BMI) in a representative sample of normal population. </p><p> <strong> Methods </strong>:This cross-sectional study was conducted as a part of a comprehensive survey, Iranian Multicenter Osteoporosis Study (IMOS), designed to assess bone health among healthy adults. Each individual underwent both L1–L4 antero-posterior lumbar spine and hip DXA scan. The difference between the T- and Z-scores measured at each of the four skeletal sites was then calculated. </p><p> <strong> Results </strong>: A -1.21 to 1.21 point difference was noted in the Z- and T- scores measured at each site. While the difference between the T- and Z-scores was less than 0.5 SD in most of the cases, the difference was higher than 1 SD in about 5% of the subjects. </p><p> <strong> Conclusion </strong>: Standardization of Z-score definition and calculation techniques as well as developing an ethnicity-matched reference population is needed to improve the reliability of DXA-generated Z-scores. </p><p>  </p> Osteoporosis, Bone Mineral Density, T-scores, Z-scores, Iran. 1016 1022 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-760&slc_lang=en&sid=1 Behnam Heidari bh.medstudent@gmail.com 200319475328460014453 200319475328460014453 No Endocrinology and Metabolism Research Center, Vali–Asr Hospital, Tehran University of Medical Sciences, Tehran, Iran. Patricia Khashayar patricia.kh@gmail.com 200319475328460014454 200319475328460014454 No Endocrinology & Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran. Mohsen Rezai Homami mohsen_rez@yahoo.com 200319475328460014455 200319475328460014455 No Rasul-Akram Hospital, Iran University of Medical Sciences Tehran, Iran. Atieh Pajouhi ap.medstudent@gmail.com 200319475328460014456 200319475328460014456 No Endocrinology & Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran. Akbar Soltani soltania@tums.ac.ir 200319475328460014457 200319475328460014457 Yes Endocrinology & Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran. Bagher Larijani larijani@tums.ac.ir 200319475328460014458 200319475328460014458 No Endocrinology & Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran.