ProblemAdenomyosis (AM) is associated with immune response and inflammation. However, the role of T cell subsets in AM development has not been thoroughly understood.Method of StudyPatients with focal or diffuse AM were recruited. Serum cytokines were quantified by enzyme‐linked immunosorbent assay (ELISA). Different T cell subsets in the blood and ectopic endometrium were determined by flow cytometry.ResultsSerum interleukin‐6 (IL‐6) and macrophage‐colony‐stimulating factor (GM‐CSF) were increased in patients with focal or diffuse AM before focused ultrasound ablation surgery (FUAS), but not after FUAS. Compared with the healthy control, the frequencies of CD8+ interferon‐gamma (IFN‐γ)‐expressing cytotoxic T lymphocytes (CTLs), interleukin‐17A (IL‐17A)‐expressing Tc17 cells, CD4+ T helper 1 (Th1) cells, and GM‐CSF‐expressing T helper (ThGM) cells were up‐regulated in the blood of patients with AM, especially those with diffuse AM. However, these changes were eradicated after FUAS. Meanwhile, the frequencies of these T cell subsets were positively correlated with the CA‐125 level. Furthermore, these T cell subsets were also increased in ectopic endometrium.ConclusionsOur study delineates for the first time the presence of CTLs, Tc17 cells, Th1, and ThGM cells in the blood and ectopic endometrium in AM. The results imply that T cell response might impact AM development.