The aim of this study was to investigate the effect of menopause on bone loss in the proximal femur and the lumbar spine. The rates of change in bone mineral density (BMD) were measured longitudinally by dual X-ray absorptiometry (DXA) at the femoral neck (FN), Ward's triangle (WT), and trochanter (TR) together with the lumbar spine in 81 healthy postmenopausal women (45-65 years of age) who had passed a natural menopause, 6 months to 12 years before. A significant correlation between the rate of change and interval since menopause was evidenced. The best fit of the data was a binomial function of interval since menopause at the spine, FN, and WT and a simple linear regression at TR level. At each skeletal site, the rate of bone loss (mean ± SD) was significantly different (p < 0.05) and twice as high in women who were between 6 months and 2 years postmenopausal at enrollment (FN, -1.82 ± 1.1.%; WT, -2.43 ± 1.7%; TR, -1.12 ± 1.7%) than in those who were beyond 5 years of menopause (FN, -0.48 ± 0.8%; WT, -0.68 ± 2.1%; TR, 0.41 ± 1.2%). A poor correlation (r = 0.39 - 0.42, p < 0.001) was found between the rate of vertebral and that of femoral postmenopausal bone loss. This study demonstrates that menopause is associated with a rapid and transient bone loss in BMD of the proximal femur, which declines with time after 3 years. These data suggest that therapy should be initiated as early as possible after menopause to prevent bone loss.