To determine the effects of different hormone replacement therapy (HRT) regimens on thyroid function in surgical menopause. STUDY DESIGN: In a randomized, controlled study, 59 euthyroid women with surgical menopause were randomized to an estrogenonly (n=20), tibolone (n=20) or calcium-only (n = 19) group. On the 5th postoperative day and 4th and 12th weeks, serum E-2, TSH, free T3 and free T4 levels were determined. RESULTS: Although the initial and week 4 serum E-2, TSH, free T3 and free T4 levels were comparable, the week 12 serum E-2 and TSH levels were different between the subjects on estrogen therapy and those receiving tibolone or calcium only (p = 0.008 and 0.000, respectively). Serum E-2 levels were higher and TSH levels lower in subjects receiving estrogen. Moreover, serum TSH levels correlated negatively with serum E-2 levels in the 12th week of estrogen use (r = -0.354, p = 0.006). TSH increased in the tibolone group as compared to the estrogen group but was still lower than in the calcium-only group; however, the differences were not statistically significant. CONCLUSION: Irrespective of different regimens, HRT does not have an important short-term effect on thyroid function in women with surgical menopause.