Background and aim: This study analyzed peripheral blood lymphocyte subsets to determine their role in the etiopathogenesis of IGM. Materials and methods: This study includes 51 pathologically proven IGM patients (active disease: 26 and in remission: 25) and 28 healthy volunteers. The analyses of lymphocyte subsets were performed by flow cytometric immunophenotyping. Results: The percentage of T helper lymphocyte of all IGM patients were lower than control groups (p = 0.001). Absolute cytotoxic T lymphocyte count (p = 0.03), both percentage (p = 0.035) and absolute count (p = 0.002) of the natural killer cells, and both percentage (p = 0.038) and absolute count (p = 0.008) of natural killer T cells, were higher than the control group. The T helper lymphocyte percentage of the patients with active disease was lower than the control group (p = 0.0003). The absolute cytotoxic T lymphocyte (p = 0.029) and natural killer T cells (p = 0.012) of the patients with active disease were higher than the control group. Conclusion: Idiopathic granulomatous mastitis is defined as a localized form of granulomatous disorders. However, the observed changes in T cells, NK, and NKT cells suggest that there is systemic immune dysregulation in patients with IGM.