Interleukin 2 signaling is believed to be critically involved in several aspects of CD25⁺ CD4⁺ regulatory T cell biology, such as intrathymic development, peripheral survival and suppressive function. Here we have analyzed the effects of interleukin 2 or CD25 deficiency on agonist-driven thymic development and the peripheral homeostasis of an antigen-specific population of regulatory T cells positive for forkhead family transcription factor Foxp3 and have correlated our observations with polyclonal suppressor populations. We found that the differentiation, acquisition of functional capacity and formation of a sizeable pool of suppressor T cells in the thymus was independent of interleukin 2 signaling, but that interleukin 2 was essential for the survival of mature Foxp3⁺ regulatory T cells.