Current thinking and available clinical data on the relationship between hyperthyroidism and bone disease are discussed. Data are also presented on TSH-suppressive and non-suppressive thyroid hormone therapy and its effect on bone. Although these data are clearly inconsistent, some risk factors for thyroid hormone induced osteopenia seem to be accepted: long standing, clinically manifest hyperthyroidism (a very rare disorder today because of early diagnosis and appropriate therapy), old age, menopause and total thyroidectomy. Thyroid hormone therapy (whether TSH-suppressive or not) has not been proven so far to lead to manifest osteoporosis.