Untreated hyperthyroidism is characterized by increased bone turnover with loss of bone and bone mineral. The aim of the present investigation was to evaluate the reversibility of these changes by measuring bone mass, bone turnover, and calcium homeostasis in surgically treated former hyperthyroid patients who had been euthyroid for at least 6 years. Sixty euthyroid former hyperthyroid patients and 94 normal sex- and age-matched controls participated. Heights and body weights and composition were similar in the two groups. In the thyroxine substituted patients (n = 27) both serum T4 and serum free T4-index (S-FT4I) were increased (p < 0.001) compared to the normal controls as well as the nonsubstituted patients. In the nonsubstituted patients. In the nonsubstituted patients (n = 33), serum TSH was increased (p < 0.001) compared to the normal controls. No significant differences were observed between substituted and nonsubstituted patients and normal controls with respect to serum T3, serum free T3-index (S-FT3I), or regional or total bone mineral content (BMC) and density (BMD) values. Serum levels of calcium, phosphate, magnesium, intact PTH, and renal excretion of calcium were unchanged. However, serum levels of 1,25-dihydroxy- and 25-hydroxyvitamin D were reduced. Urinary excretion of hydroxyproline was increased by 16% (p < 0.05), but serum cross-linked carboxy-terminal teleopeptide of type I collagen (ICTP) was decreased by 11% (p < 0.01). Urinary excretion of collagen cross-links was normal. Serum levels of osteocalcin, carboxy-terminal propeptide of human type I procollagen (PICP), and total and bone alkaline phosphatase were all normal. In conclusion, surgically treated former hyperthyroid patients have normal bone mass, bone turnover, and calcium homeostasis in spite of minor variations in thyroid hormones and vitamin D metabolites.