Systemic and local inflammatory processes have a key, mainly detrimental role in the pathophysiology of ischemic stroke. Currently, little is known about endogenous counterregulatory immune mechanisms. We examined the role of the key immunomodulators CD4⁺CD25⁺ forkhead box P3 (Foxp3)⁺ regulatory T lymphocytes (T_reg cells), after experimental brain ischemia. Depletion of T_reg cells profoundly increased delayed brain damage and deteriorated functional outcome. Absence of T_reg cells augmented postischemic activation of resident and invading inflammatory cells including microglia and T cells, the main sources of deleterious cerebral tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), respectively. Early antagonization of TNF-α and delayed neutralization of IFN-γ prevented infarct growth in T_reg cell–depleted mice. Intracerebral interleukin-10 (IL-10) substitution abrogated the cytokine overexpression after T_reg cell depletion and prevented secondary infarct growth, whereas transfer of IL-10–deficient T_reg cells in an adoptive transfer model was ineffective. In conclusion, T_reg cells are major cerebroprotective modulators of postischemic inflammatory brain damage targeting multiple inflammatory pathways. IL-10 signaling is essential for their immunomodulatory effect.