This review discusses the abnormalities in bone and mineral metabolism encountered in thyroid disorders. Thyroid hormones probably stimulate bone resorption directly, thereby increasing serum calcium and phosphorus concentrations and suppressing serum parathyroid hormone and 1,25-dihydroxyvitamin D3 concentrations. The decrease in these bone-resorbing hormones limits further increase in serum calcium concentration but also results in an enhanced intestinal calcium absorption. Such a negative calcium balance will eventually lead to hyperthyroid osteopenia. In adult hypothyroidism the opposite effects are seen.