The World Health Organisation (WHO) has proposed a set of guidelines for the diagnosis of osteoporosis in adult women based on a measurement of bone mineral density (BMD) expressed as the number of SD below young adult mean (t-score). In this study, we investigated the number of subjects classified as either osteopenic or osteoporotic according to these guidelines using dual X-ray absorptiometry (DXA), at the hip, at the spine and at the lower forearm and quantitative ultrasound (QUS), at the heel. A total of 247 men, 209 postmenopausal women and 195 premenopausal women were included in the study. Furthermore, the study provides the first normative data showing the influence of sex, age and menopause on broadband ultrasound attenuation (BUA) and speed of sound (SOS), as measured by the DTU-one imaging ultrasound scanner. The difference between the number of patients classified into either diagnosis group by the investigated parameters is large ranging from 25·9% of the women being diagnosed as osteopenic by BUA at the heel to 43·0% by BMD at the femoral neck. For men, the same range is from 20·5% by BUA to 44·1% by BMD at the femoral neck. For the classification into the osteoporotic group, the range is from 2·5% by intertrochanteric BMD to 24·4% by BMD at Ward’s triangle for women and from 0% by SOS to 29·0% by BMD at Ward’s triangle for men. Using total hip BMD as the reference parameter to categorize the subjects as normal, osteopenic or osteoporotic, the agreement of the other parameters with this classification is assessed in terms of sensitivity and specificity. We conclude that there are significant differences in the classification of osteoporosis/osteopenia depending on the site measured and the technique used for the bone mass assessment. Furthermore, we suggest that development of technique and site specific cut-off values may increase the accuracy of the classification of osteoporosis/osteopenia in both men and women.