CD4(+) T cells play a central role in initiating and maintaining anticancer immune responses. However, regulatory CD4(+)CD25(+) T cells which express Foxp3 have also been shown to inhibit antitumor effector T cells. In view of these heterogeneous CD4(+) T-cell populations, this study was designed to determine the prognostic value of various tumor-infiltrating CD4(+) T-cell populations in head and neck squamous cell carcinoma.