The influence of age and physique on dual-energy X-ray absorptiometry (DXA) and quantitative ultrasound (QUS) was investigated in young, middle-aged, and older women. The validity of the bilateral calcaneal QUS values was investigated regarding the bone mineral density (BMD) values on DXA of the lumbar spine, left femoral neck, and left femur as the optimal standards. The subjects were 55 young women (19.6 +/- 1.0 years), and 152 middle-aged and older women (62.9 +/- 7.2 years). The BMD on DXA was significantly correlated with the bone strength on QUS in both young and middle-aged or older women, but the positive likelihood ratios of the standard QUS values recommended by the manufacturer to the optimum standards on DXA were low, suggesting that osteoporosis cannot be diagnosed or predicted by use of the QUS method. Combination with DXA is necessary, such as primary screening by QUS followed by secondary screening by DXA.