XAGE-1b is a cancer/testis antigen that has been shown to be expressed at a significant frequency and to be immunogenic in non-small cell lung cancer (NSCLC). In the present study, we investigated correlations between XAGE-1b expression and NSCLC patient survival. XAGE-1b expression was examined immunohistochemically using USO9-13, an anti-XAGE-1b monoclonal antibody, in 121 NSCLCs (83 adenocarcinomas and 38 other histological types). XAGE-1b expression was observed in 27 (32.5%) adenocarcinoma specimens. In the other histological types, positive staining was observed in only 1 specimen. HLA class I expression in these samples was assessed previously. XAGE-1b expression had no correlation with overall survival. However, both XAGE-1b and HLA class I expression correlated with prolonged survival (P = 0.019). Moreover, expression of XAGE-1b combined with down-regulated HLA class I expression correlated with poor survival (P = 0.01). The density of cancer nest-infiltrating CD8+ T-cells in tumors expressing both XAGE-1b and HLA class I was higher than that in other groups. The findings suggest that XAGE-1b and HLA class I expression elicited a CD8+ T-cell response against minimal residual disease after surgery and resulted in prolonged survival of NSCLC patients.