The thyroid gland is susceptible to nodulation. The mechanism responsible for the growth of only some follicular cells, which results in nodule formation, is not yet clear. Selenium deficiency may be a risk factor in the development of thyroid nodules. The aim of this study was to investigate the relationship between selenium levels in patients with euthyroid nodular thyroid disease. Seventy patients with a solitary euthyroid thyroid nodule, 70 patients with more than one euthyroid nodule, and 60 healthy patients without thyroid nodules were included in the study. Venous serum samples were stored at -80°C and analyzed the same day using spectrometry. The selenium levels of patients with multiple thyroid nodules, solitary nodules, and patients without nodules were 57.3 ± 14.8 μg/L; 58.8 ± 15.1 μg/L; and 57.6 ± 13.3 μg/L, respectively. The mean serum selenium level of all patients included in the study was 57.9 ± 14.4 μg/L. Although serum selenium levels were slightly higher in men, a statistically significant difference was not observed. In our study, a significant relationship between serum selenium levels and nodular thyroid disease was not seen. Our study was undertaken in an iodine sufficient region. Mean serum selenium levels were lower compared with many other studies, which may be associated with the low selenium content of the soil. Nodular thyroid disease shows multifactorial features. When our study is considered together with previous studies, serum selenium levels may considered to be effective on structural thyroid diseases if combined with additional factors such as severe iodine deficiency. Further studies are required to assess the role of selenium in thyroid nodule formation.