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Graves' disease (GD) is one of the most common autoimmune conditions, but the mechanisms underlying the associated induction of autoimmunity are not known. We explored the role of peripheral lymphocyte subpopulations in disease pathogenesis. In total, 32 patients and 40 age- and sex-matched healthy controls were recruited in this study. Peripheral levels of T, B, NK, CD4+ T, CD8+ T, Th1, Th2, Th17, and Treg cells were measured using flow cytometry. For all patients, we compared all lymphocyte subpopulations between GD patients and healthy controls. Changes in patient lymphocyte subsets were compared before and after treatment. The absolute numbers of circulating Th17 cells (0.45 ± 1.16, p > 0.05) between GD patients and healthy controls were not significantly different. However, the percentage of Th17 cells was significantly increased (0.25 ± 0.11, p < 0.05). The absolute numbers and percentages of circulating Tregs in GD patients were significantly decreased compared with those in healthy participants (11.61 ± 2.75, p < 0.05). There was a significant difference in Treg absolute numbers between the untreated and drug-treated groups. Furthermore, we found that the Treg percentage in untreated patients (mean=4.78) was not significantly different from that in the drug-treated group (mean=4.81). In addition, circulating Treg absolute numbers in GD patients with exophthalmos were significantly lower than those in GD patients without exophthalmos (9.96 ± 4.16, p < 0.05). A similar trend was observed in GD patients with weight loss (11.97 ± 3.28, p < 0.05). GD pathogenesis was associated with a lower Treg population and an increased Th17/Treg ratio (T helper cell 17/ regulatory T cells). Th17 cells in this study were not related to the disease. Furthermore, anti-thyroid drug therapy improved immune-mediated system disorders. Finally, we found lower absolute numbers of circulating Tregs in GD patients with certain positive signs, such as exophthalmos and/or weight loss. Thus, immune changes are correlated with partial clinical manifestations. • The pathogenesis of Graves'disease is associated with lower Treg absolute counts and increased ratio of Th17/Treg. • Th17 cells in this study were proved to be not related to the disease. • Antithyroid drug therapy may improve immune-mediated system disorders to some extent. • The absolute counts of Tregs in peripheral blood of Graves'disease patients with some positive signs was reduced. [ABSTRACT FROM AUTHOR]