Thyrotoxicosis, commonly seen in a condition with Graves' disease, causes increased bone absorption and results in osteoporosis with increased bone turnover. The osteoporotic state is dominant in cortical bones with slight impairment of calcium-homeostasis, although the precise mechanism is still elusive. It ought to be recovered in accordance with the amelioration of thyroid hormone status, but past history of thyrotoxicosis might cause bone fragility, especially in post-menopausal or senile patients.