Impaired cell-mediated immunity has been consistently demonstrated in patients with advanced head and neck squamous cancer (HNSC); however, the results of prior studies of correlations of cellular immune parameters with treatment outcome have been inconsistent, and routine assessment of immune parameters has been of limited clinical use. To determine the prognostic importance of alterations in the proportions of various T-lymphocyte subpopulations in the peripheral blood of patients with HNSC, levels of T3, T4, T6, T8, T9, T10, T11, and Leu 7 cells were quantitated by flow cytometry in 80 previously untreated patients and prospectively correlated with tumor characteristics and clinical course (median length of follow-up, 27 months). The mean helper/suppressor cell ratio (T4/T8) increased progressively with increasing tumor stage and was significantly elevated among patients with cancer as a group and in patients with advanced (stage III or IV) disease compared with 40 normal subjects. Decreased disease-free survival was significantly associated with elevated T4/T8 ratios and low percent T8 and T11 cell levels. The prognostic significance of percent T8 (cytotoxic/suppressor) cell levels persisted even after adjusting for known prognostic factors of tumor stage, T class, N class, and tumor site. These correlations provide new insight into immune alterations in HNSC that may prove useful in identifying patients with early clinical disease who have a poor prognosis.