Infection with West Nile virus (WNV) causes fatal encephalitis more frequently in immunocompromised humans than in those with a healthy immune system. Although a complete understanding of this increased risk remains unclear, experiments with mice have begun to define how different components of the adaptive and innate immune response function to limit infection. Previously, we demonstrated that components of humoral immunity, particularly immunoglobulin M (IgM) and IgG, have critical roles in preventing dissemination of WNV infection to the central nervous system. In this study, we addressed the function of CD8+ T cells in controlling WNV infection. Mice that lacked CD8+ T cells or classical class Ia major histocompatibility complex (MHC) antigens had higher central nervous system viral burdens and increased mortality rates after infection with a low-passage-number WNV isolate. In contrast, an absence of CD8+ T cells had no effect on the qualitative or quantitative antibody response and did not alter the kinetics or magnitude of viremia. In the subset of CD8+-T-cell-deficient mice that survived initial WNV challenge, infectious virus was recovered from central nervous system compartments for several weeks. Primary or memory CD8 + T cells that were generated in vivo efficiently killed target cells that displayed WNV antigens in a class I MHC-restricted manner. Collectively, our experiments suggest that, while specific antibody is responsible for terminating viremia, CD8+ T cells have an important function in clearing infection from tissues and preventing viral persistence.