Abstract: Increased thyroid hormones level is associated with diminished bone density. It has been clarified that thyroid hormones by sirculating bone resorption lead to decrease in bone density. Thyroid hormone in many cases as in Non - Toxic Grotre & in supplement therapy in hypothyroidism is used as a drug & it is possible that suppressive therapy with T4 causes subclinical - hyperthyroidism. Studies done in west has shown different results regarding the effect of this therapy on bone density. Since thyroid diseases are very common in our country & suppressive therapy for thyroid disturbance in used frequently, in this study effect of suppressive therapy with thyroid hormones on bone density is studied in an area endemic in thyroid diseases. In this study 30 ladies who had been treated with thyroid hormones for Non-toxic Goiter for at least one year were studied. All patients had TSH below normal level & for 10 of them stimulation test of TRH done that was reported as non - responsitiveness that shows the dose has been enough for suppressive therapy. Information was taken from patients about BMI , the duration of the illness, amount of calcium cafeine intake & activity . At last measurement of bone density with DEXA method was performed for patients & its result was compared with Iranian standard & International standard were used. There was no significant change in spine and femoral Bone density during 1 year period. The BMD differences at the radios were significant . In conclusion, our data indicate that in premenopausal women suppressive therapy is not associated with bone loss in femur and spine during the first year of treatment . For definitive conclusion a longer studding is recommended.