The objective of our study was to compare bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) and quantitative ultrasound (QUS) parameters in women with hyperthyroidism and controls. In this cross-sectional study, QUS parameters and BMD values observed in untreated hyperthyroid patients were compared with data obtained from age-matched controls. Twenty-four women with Graves' disease were studied. Eight patients were postmenopausal. All patients had evidence of thyrotoxicosis as indicated by a raised total serum thyroxine and a suppressed serum thyroid stimulating hormone. BMD of the hip, lumbar spine and whole body, and body composition, were measured by DXA. Ultrasound evaluation on the os calcis was performed with an Achilles device. All measurements were performed before antithyroid therapy. The QUS parameters of BUA, SOS and Stiffness were significantly lower in hyperthyroid patients than in controls. Similar results were observed for the BMD of lumbar spine, femoral neck and total skeleton. Lean tissue and fat mass were also significantly decreased in hyperthyroid patients. In conclusion, these findings suggest that hyperthyroidism affects cortical and trabecular bone equally, as well as bone quality. QUS measurements may be helpful for assessing, using a simple and non-irradiating method, the bone effects of thyrotoxicosis.