Abstract Low trauma fractures in the elderly are highly predictable by measurement of bone mineral density (BMD). Preventive measures for low BMD, such as hormone replace therapy (HRT), have potential risks. Thus, a rational decision on HRT or other therapy critically depends on an accurate diagnosis of osteopenia/osteoporosis. We assessed the degree of diagnostic heterogeneity based on spine and hip BMD for 2313 women. We found: 1. In ∼30.0% of cases, the difference between spine and hip Z- and T-scores was >1.0, and in 20.8% (Z-scores) and 15.2% (T-scores) the difference was >2.0. 2. With increasing age, the proportions of women with Z- or T-scores greater at the hip than the spine generally decreased. 3. The correlation between hip and spine and Z- and T-scores ranged from 0.50 to 0.72, and generally decreased with increasing age. 4. If screened only at the hip or spine, 17.9/27.3% with osteopenia and 1.3/2.9% with osteoporosis at either site would be diagnosed as normal. Corresponding analyses of 143 men yielded similar results. Therefore, if possible, dual X-ray absorptiometry (DXA) of both the spine and hip should be performed for an accurate assessment of osteoporosis at these two most frequently fractured sites. If only one site is chosen, measurement of the hip is preferred to measurement of the spine.