This study sought to determine whether the in situ tumor-infiltrating immune lymphocytes, as a novel companion to the Immunoscore analysis, could be a promising, valuable prognostic and predictive marker in patients with head and neck squamous cell carcinoma (HNSCC). Total (CD3+) and cytotoxic (CD8+) T lymphocytes were assessed using immunohistochemistry in tumor nests and stroma obtained from patient surgical specimens. The “Immunoscore” methodology has been defined to quantify the amount of in situ immune infiltrate (from I0 to I4). Survival curves were measured using the Kaplan–Meier method, and differences in survival and response to therapy between the groups were estimated using the log-rank test. The prognostic value of the Immunoscore was determined using Cox multivariate analysis. The density and location of CD3+ and CD8+ lymphocytes and the associated Immunoscore correlated significantly with differences in disease-free survival (DFS) and overall survival (OS) (all P < .005). Compared with tumor-node-metastasis (TNM) staging, the Immunoscore was found to have an advantage in predicting survival (P = .000). In addition, a high Immunoscore was associated with the tumors of advanced-stage patients who underwent different treatment regimens. The Immunoscore could be a useful prognostic marker. The measurement of CD3+ and CD8+ cell infiltration may be beneficial in HNSCC patients and may help determine which patients may benefit most from definitive chemoradiotherapy. •Established an Immunoscore system in resected HNSCC patients.•The Immunoscore system was able to predict the prognosis of HNSCC.•The Immunoscore were the supplementation of TNM staging.•Immunoscore is used to determine the treatment plan for patients with HNSCC.