The RAS signaling pathway is constitutively activated in psoriatic keratinocytes. We expressed activated H-RAS V12G in suprabasal keratinocytes of adult mice and observed rapid development of a psoriasis-like skin phenotype characterized by basal keratinocyte hyperproliferation, acanthosis, hyperkeratosis, intraepidermal neutrophil microabscesses, and increased T helper type 1 (Th1)/Th17 and T cell type 1 (Tc1)/Tc17 skin infiltration. The majority of skin-infiltrating CD8 + T cells coexpressed IFN-γ and IL-17A. When RAS was expressed on a Rag1-/- background, microabscess formation, inducible nitric oxide synthase expression, and keratinocyte hyperproliferation were suppressed. Depletion of CD8 +, but not CD4 +, T cells reduced cutaneous and systemic inflammation, the RAS-induced increase in cutaneous Th17 and IL-17 + γδ T cells, and epidermal hyperproliferation to levels similar to a Rag1-/- background. Reconstitution of Rag1-/- inducible RAS mice with purified CD8 + T cells restored microabscess formation and epidermal hyperproliferation. Neutralization of IFN-γ, but not of IL-17A, in CD8 + T-cell-reconstituted Rag1-/- mice expressing RAS blocked CD8-mediated skin inflammation, inducible nitric oxide synthase expression, and keratinocyte hyperproliferation. These results show that CD8 + T cells can orchestrate skin inflammation with psoriasis-like pathology in response to constitutive RAS activation in keratinocytes, and this is primarily mediated through IFN-γ.