Characteristics of osteoporosis occurring after menopause and oophorectomy are described. Changes in hormone dynamics induced by menopause or oophorectomy lead to high metabolic turnover of bone, characterized by increased bone formation and resorption. The increase in bone resorption surpasses that of bone formation, resulting in decreased bone mineral density (BMD). Even before the onset of menopause, a transient decrease in estrogen concentrations can produce decreases in BMD that are comparable to those occurring after menopause or oophorectomy. Long-term observation of women undergoing premature menopause indicates that BMD progressively continues to decline in association with high bone metabolic turnover. There was no significant difference between BMD, 3 years after menopause, compared with that 3 years after oophorectomy, a time when the effect on BMD are fully evident. These findings indicate that osteoporosis, associated with either menopause or oophorectomy, can be managed in the same manner in a clinical setting.