Background: The therapeutic administration of ¹³¹I for thyroid remnant ablation and for metastases comes up with some adverse effects. This study was conducted to investigate whether single high dose radioiodine therapy affects lacrimal gland functions or not. Materials and Methods: Seventy-eight eyes of 39 patients, who were diagnosed as differentiated thyroid carcinoma, were objectively tested with Schiermer’s test and tear film break-up time test before and 1 and 6 months after high dose (&ge 3700 MBq) ¹³¹I therapy. Results: The median values of pre-treatment Schiermer’s test were 10.00 mm and 9.60 mm for right and left eyes, respectively. At the post-treatment first and sixth months, no significant change was observed in the median values of Schiermer’s test in both eyes (p= 0.189 and p=0.085, respectively, Friedman test). The median values of pre-treatment tear film break-up time test were 9.15 sn and 9.20 sn for right and left eyes, respectively. The median values of post-treatment tear film break-up times reduced at first and sixth months and the difference between the pre-treatment and post-treatment values were significant in both eyes (p=0.020 and p=0.022 for right and left eyes, respectively, Friedman test). Conclusion: Impairment of goblet cell function occurs early after administration of single high dose ¹³¹I application. However, reduction in tear secretion from lacrimal gland is not observed.