The aim of this study was to evaluate the association between postmenopausal osteoporosis and kidney-vacuity syndrome. Eighty-one postmenopausal women were enrolled; their age were between 40 to 65 years old. The mean ages of the non-osteoporosis group and osteoporosis group were 54.0 +/- 4.8 and 58.9 +/- 5.9 years old, respectively. Bone density examination was performed by DEXA technique and the diagnosis of osteoporosis was made by finding 2.5 standard deviations below the bone density of healthy youths. Kidney-vacuity syndrome was deduced according to the diagnostic criteria developed in the National Congress on Chinese Medicine and Sine-Western Combined Geriatric Medicine held in the People's Republic of China in 1986. The results showed that patients with kidney-qi-vacuity and kidney-yin-vacuity were more likely to have osteoporosis than those who were not. No significant difference in the rates of osteoporosis between the kidney-yang-vacuity group and non-kidney-yang-vacuity group was found. The kidney-qi-yin-vacuity group had a higher probability of developing osteoporosis than the kidney-qi-vacuity or kidney-yin-vacuity group. By logistic regression analysis, patients with kidney-qi-vacuity or kidney-yin-vacuity were more likely to develop osteoporosis than those who were not. In conclusion, a marked association between kidney-vacuity syndrome and postmenopausal osteoporosis was observed. Patients with kidney-qi-yin-vacuity syndrome were more likely to get osteoporosis than those with kidney-qi-vacuity syndrome or kidney-yin-vacuity syndrome.