The immune system protects from cancer, however immune function declines with age and most cancers, including lung cancer and mesothelioma, emerge in people aged greater than 60 years old. Our studies in young mice (6–8 week old, cf 14-16 human years) have shown that chemotherapies used for thoracic cancer require a functional T cell response to elicit an effective anti-cancer outcome, yet T cells become increasingly dysfunctional with ageing. Therefore, we aimed to determine if chemotherapy in the elderly also requires T cells. We found that tumours grew faster in elderly mice (24–27 month old, cf 70-80 human years). This was associated with decreased muscle and body weight loss, and increased liver enzymes, implying that elderly mice are more susceptible to cancer cachexia. Chemotherapy induced even more weight loss in elderly but not young mice, and was not as effective in elderly as it was in young mice. An in-vivo CFSE-based CTL assay revealed that unlike their younger counterparts which generated a significant endogenous tumour-specific CD8+ CTL response, elderly mice generated only a weak response to dominant tumour epitopes during tumour progression. However, T cell responses to subdominant tumour epitopes in elderly mice were at least as good as those in young mice. Moreover, T cell depletion studies showed that chemotherapy in elderly mice still requires T cells to induce tumour regression. Future studies will determine if rescuing T cell function in the elderly improves their anti-cancer response to chemotherapy.