Because of pronounced symptoms and early detection, severe hyperthyroidism is usually treated before skeletal symptoms are evident. However, previous hyperthyroidism may involve a risk of later postmenopausal or senile osteoporosis, since some of the bone loss apparently is irreversible. Borderline hyperthyroidism in clinically euthyroid patients may induce accelerated bone loss and thereby increase the risk of low-energy fractures. Moreover, it is unknown whether interindividual differences exist in skeletal sensitivity to circulating thyroid hormones and thereby in the rate of bone loss. From these considerations it appears that disturbed thyroid function may be involved in the pathogenesis of osteoporosis, one of the major health problems in the western hemisphere.