The etiology of Graves ophthalmopathy (GO), representing the most common extrathyroidal manifestation of Graves disease, is multifactorial. Among multiple genetic, environmental, and endogenous factors, cytokines play a critical role in its etiopathogenesis. We studied an effect of glucocorticoid therapy on the serum IL-6, IL-4, and IL-13 levels in 18 GO patients. All the patients presented euthyroid GO with over 4 points according to the CAS classification (range 4-6; mean 4.94). The patients were treated with methylprednisolone (1 g every second day for three times) followed by 6 months oral prednisone (60 mg/day, with gradual reduction). The clinical examination (Clinical Activity Score and the GO severity by modified NOSPECS classification) and measurement of anti-TPO, anti-TG, anti-TSHR (TRAK), IL-6, IL-4, as well as IL-13 serum levels were performed before, after 2 weeks, and after 6 months of the glucocorticoid therapy. Significant serum IL-6 increases (p < 0.001) and moderate serum IL-4 and IL-13 increases (p < 0.05) were found in GO patients compared with healthy controls. After 2 weeks of the therapy, the serum IL-6 levels decreased in majority of the patients, however after 6-month observation, lower serum IL-6 levels were only in 8 patients who seemed to respond clinically to the therapy (mean value of the Clinical Activity Score decreased from 4.5 before the therapy initiation to 1.25 after 6 months of the glucocorticoid therapy). No changes in IL-4 and IL-13 serum levels during the therapy were observed. Statistical analysis revealed a good correlation between serum IL-6 level and the Clinical Activity Score (p < 0.01). Based on the obtained data, we conclude that IL-6 plays an important role in GO. It seems that IL-6 may serve as a useful factor in the inflammatory events of GO.