Significance T-cell homeostasis is a tightly regulated process that ensures a constant number of naïve T cells in the periphery of an organism. Mechanisms that promote the survival and homeostatic proliferation of naïve peripheral T cells are essential for maintaining this balance and thus effective immunity against pathogens and incipient tumors. We have identified UV radiation resistance-associated gene (UVRAG), an autophagic tumor suppressor in many cell lineages, as a novel nonautophagic regulator of naïve peripheral T cell homeostasis. Furthermore, our findings distinguish UVRAG from other autophagy-related genes and indicate that this regulator may have important nonautophagic functions that are cell type-specific.