We compared bone mass in premenopausal, perimenopausal, and postmenopausal women using peripheral quantitative computed tomography to measure separately cortical, trabecular, and total bone density. Trabecular bone density was lower (p < 0.05) in the perimenopausal women than in the healthy premenopausal women. In perimenopausal women, trabecular bone density showed a significant linear regression with age (r = 0.554, p < 0.001), but cortical bone density did not (r = 0.130, p = 0.447). The group of postmenopausal women had significantly lower bone mass in all three bone compartments than the premenopausal and perimenopausal women. These findings confirm the existence of a significant loss of trabecular bone mass in the perimenopausal period.