We investigated intratumoral tumor‐infiltrating lymphocytes (TILs), including CD4⁺ and CD8⁺ T cells, in non‐small cell lung cancers (NSCLCs) and their relationships with clinicopathological variables and post‐operative survival. Tumor specimens from 178 NSCLCs were consecutively obtained by surgery at the Hokkaido University Medical Hospital between 1976 and 1994. CD8⁺ T cells, CD4⁺ T cells and Ki‐67/CD8⁺ T cells were visualized immunohistochemically, and counted within cancer cell nests and in cancer stroma. CD8⁺ T cells and CD4⁺ T cells were observed at higher frequencies within cancer cell nests in moderately and poorly differentiated tumors compared with well differentiated tumors (P<0.01), and in tumors with high Ki‐67 expression compared with low Ki‐67 expression (P<0.01), that showed severe cellular atypia and a higher growth rate. Patients with higher numbers of CD8⁺ T cells within cancer cell nests showed significantly shorter survival times compared to those with lower numbers of CD8⁺ T cells within cancer cell nests (5‐year survival rates, 47% and 60%, respectively; P=0.03). Moreover, patients with higher labeling index of Ki‐67/CD8⁺ T cells showed significantly shorter survival than those with lower labeling index of Ki‐67/CD8⁺ T cells within cancer cell nests (5‐year survival rates, 41% and 69%, respectively; P=0.02), and the labeling index of Ki‐67/CD8⁺ T cells within cancer cell nests was found to be a significant and independent unfavorable prognostic factor by multivariate analysis (P=0.01). On the other hand, higher numbers of CD4⁺ T cells in cancer stroma, but not within cancer cell nests, were correlated with longer survival times in patients with NSCLC (5‐year survival rates, 64% and 43%, respectively; P=0.04). CD4⁺ T cells in cancer stroma might reflect immune responses against cancer cells, while CD8⁺ T cells do not appear to work as effectors in tumor tissues of NSCLC. Moreover, the higher labeling index of Ki‐67/CD8⁺ T cells within cancer cell nests is a strong indicator of unfavorable clinical outcome.