Bone mineral density (BMD) of the lumbar spine was measured in 286 women (46-55 years of age) using dual photon absorptiometry. The women were classified in three categories: premenopausal, perimenopausal and postmenopausal. The postmenopausal group was subdivided according to the number of years since the last uterine bleeding. with multiple linear regression analysis of lumbar BMD on age and menopausal status, an acceleration of bone loss was observed during the perimenopausal period and the following first two postmenopausal years. No significant bone loss was detected in relation to age or during the later postmenopausal years. Applying both an additive and a multiplicative model of bone loss, the mean perimenopausal bone loss was 0.061 gramequivalents hydroxyapatite (geqHA)/cm2 and 6.4%, respectively. In the first 2 postmenopausal years the mean bone loss was 0.044 geqHA/cm2 and 5.1% per year. These results suggest a substantial menopause related acceleration of lumbar bone loss in a relatively short time span with its onset in the perimenopausal period. © 1988.