Th17 cells are newly identified effector CD4(+) T cells, which play an active role in inflammation and autoimmune diseases and may be relevant for anti-tumor defenses. In the present study, we examined expression of Th17 cells in specimens of breast cancer tissue and its association with clinical, pathology, and immunological parameters. Expression rates of Th17 and T regulatory (Treg) cells in breast cancer and normal (i.e. non-cancerous) tissue were evaluated using flow cytometry in 30 patients with breast carcinoma. Further, expression of interleukin-17 (IL-17), interleukin-1 beta (IL-1 beta), and interleukin-6 (IL-6) in breast cancer tissue was evaluated by immunohistochemical staining. Associations between Th17 expression and other parameters were analyzed by multiple linear regression analysis. We observed that expression of Th17 cells was significantly higher in breast cancer compared to normal breast tissue. Further, expressions of IL-17, IL-1 beta, and IL-6 in cancer tissue positively correlated with expression of Th17 cells. In addition, there was a negative association between the numbers of Th17 cells and TNM stage, blood vessel invasion, and increased numbers of metastatic lymph nodes. Finally, expression of Th17 was not associated with expression of Treg. In conclusion, Th17 cells appear to be involved in anti-tumor immune responses and are associated with a more favorable prognosis.