Infection with one of the four serotypes of dengue virus (DENV1–4) can result in a range of clinical manifestations in humans, from dengue fever to the more serious dengue hemorrhagic fever/dengue shock syndrome. Although T cells have been implicated in the immunopathogenesis of secondary infections with heterologous DENV serotypes, the role of T cells in protection against DENV is unknown. In this study, we used a mouse-passaged DENV2 strain, S221, to investigate the role of CD8+ T cells in the immune response to primary DENV infection. S221 did not replicate well in wild-type mice, but did induce a CD8+ T cell response, whereas viral replication and a robust CD8+ T cell response were observed after infection of IFN-α/βR−/− mice. Depletion of CD8+ T cells from IFN-α/βR−/− mice before infection resulted in significantly higher viral loads compared with undepleted mice. Mapping the specificity of the CD8+ T cell response led to the identification of 12 epitopes derived from 6 of the 10 DENV proteins, with a similar immunodominance hierarchy observed in wild-type and IFN-α/βR−/− mice. DENV-specific CD8+ T cells produced IFN-γ, TNF-α, expressed cell surface CD107a, and exhibited cytotoxic activity in vivo. Finally, immunization with four of the immunodominant CD8+ T cell epitopes enhanced viral clearance. Collectively, our results reveal an important role for CD8+ T cells in the host defense against DENV and demonstrate that the anti-DENV CD8+ T cell response can be enhanced by immunization, providing rationale for designing DENV-specific vaccines that induce cell-mediated immunity.