Osteoporosis may be induced by hyperthyroidism through an increase of bone turnover, because bone resorption exceeds formation in this condition. Also therapy with 1-thyroxine, especially by TSH-suppressive doses, may induce a reduction in bone mineral content. Circulating osteocalcin (sBGP) significantly increases both in endogenous and exogenous hyperthyroxinemia and is considered a reliable non invasive marker of bone turnover. In this study an extra-increase of sBGP in hyperthyroid post-menopausal women towards pre-menopausal is reported, the persistence of high sBGP levels in patients affected by any type of hyperthyroidism after four months of therapy and a positive relationship with thyroid hormones (fT4). Therefore monitoring of this serum marker may be suggested also in patient chronically treated with 1-thyroxine to avoid, if possible, overzealous therapy.