In this cross-sectional study, bone mineral density (BMD) measurements were performed in 1762 ambulatory subjects (678 men and 1084 women) aged 55 years and over from the Rotterdam Study, a population based study of diseases in the elderly. BMD measurements of the proximal femur and lumbar spine were performed using dual energy X-ray absorptiometry. No age-related decline in BMD could be observed in the lumbar spine. Yearly percentage BMD reduction in women and men was −0.6% and −0.3% in the femoral neck, −0.8% and −0.5% in the Ward's triangle, and −0.4% and −0.3% in the trochanter, respectively. Late menopause was associated with high BMD in Ward's triangle and lumbar spine. We conclude that: (1) accurate assessment of age-related bone reduction in the spine is impossible from cross-sectional studies since BMD measurements in the elderly may be influenced by spinal osteoarthritis; and (2) the rate of age-related bone reduction in the femoral neck appears to be approximately two times higher in women than in men.