Lymphocytes residing in the intestinal epithelium are exclusively T cells and account for one of the largest collection of T cells in the organism. However, their function remains obscure. We and others have shown that the development of intestinal intraepithelial T cells is compromised in mutant mice prone to chronic intestinal inflammation. These results led us to directly assess their role in regulating the development of colitis secondary to transfer of primary splenic TCRαβ⁺CD4⁺CD45RB^hi T cells into severe combined immunodeficiency (SCID) mice. Here we demonstrate that prior reconstitution of SCID recipients with intraintestinal TCRαβ⁺CD4⁻CD8α⁺β⁻ T cells prevents disease, and does so in an interleukin (IL)-10–dependent fashion. In contrast, reconstitution with either TCRγδ⁺ or TCRαβ⁺CD4⁻ CD8α⁺β⁺ intestinal T cells did not prevent colitis. TCRαβ⁺CD4⁻8α⁺β⁻ T cells are unique to the intestinal epithelium of both rodents and humans. Previous repertoire analyses of TCRαβ⁺CD4⁻CD8α⁺β⁻ T cells revealed a high proportion of cells expressing high affinity, self-specific TCR within this subset. We demonstrate that monoclonal, self specific TCRαβ⁺CD4⁻CD8α⁺β⁻ cells derived from TCR transgenic mice also prevent the onset of colitis. Thus, intestinal TCRαβ⁺CD4⁻CD8α⁺β⁻ T cells, selected based on their self-reactivity, maintain gut integrity in a IL-10–dependent fashion.