The bone mineral density (BMD) of the lumbar spine and proximal femur was measured using dual-energy X-ray absorptiometry in 717 healthy women aged 20-70 years. The maximal mean BMD was found at the age of 35-39 years in the spine and at the age of 20-24 in the femoral neck and Ward's triangle. No significant change in lumbar BMD was found from the age of 20 to 39 years. The spinal BMD values were relatively stable from age 20 to 39 years, whereas a linear decrease in BMD in the femoral neck and Ward's triangle was already apparent in the youngest age group (20-24 years). The major fall in BMD in all sites was related to the menopause. The overall decreases in BMD from the peak values to those at age 65-70 years were 20.4%, 19.0% and 32.6% in the lumbar spine, femoral neck and Ward's triangle, respectively. The correlation of trochanteric BMD with age was poor. BMD was positively correlated with weight in all measurement sites. Nulliparity was found to be a risk factor for osteoporosis. The present study confirmed that the menopause has a significant effect not only on spinal BMD but also on femoral BMD. Lumbar BMD was lower and BMDs in the proximal femur were higher in Finnish women than in white American women. This emphasizes the importance of national reference values for BMD measurements.