So far, very little is known on the impact of rTMS on hypothalamo-pituitary-thyroid axis.2 A slight increase in plasma TSH level, remaining in the normal ranges, has been reported in healthy volunteers and in depressed patients with HF-rTMS (5 Hz to 20 Hz).1,3,4 In our present case, we report a significant increase in plasma TSH, above normal range, during LF-rTMS (1 Hz) treatment. Because our patient had a history of thyroidectomy, this rise in TSH did not induce any increase in plasma T4 level. In patients with a normal thyroid gland, we may expect an increase in plasma T4 secondary to the LF-rTMS-induced rise in plasma TSH. Such an increase in plasma T4 level has been recently suspected by Osuch et al.5 during treatment of anxiety disorders by LF-rTMS. Thus, rTMS can have significant effects on the pituitary-thyroid axis that may potentially induce hyperthyroidism. Further studies are needed to assess the effects of rTMS on thyroid function.