Recent studies have suggested a close relationship between CD4(+)FOXP3(+) regulatory T cells (Tregs) and proinflammatory IL-17-producing T helper cells (T(H)17) expressing the lineage-specific transcription factor RORgamma t. We report here the unexpected finding that human memory Tregs secrete IL-17 ex vivo and constitutively express RORgamma t. IL-17-secreting Tregs share some phenotypic and functional features with conventional T(H)17 cells, expressing high levels of CCR4 and CCR6 and low levels of CXCR3. However, unlike conventional T(H)17 cells, they express low levels of CD161 and mostly fail to cosecrete IL-22 and TNF-alpha ex vivo. Ex vivo secretion of IL-17 and constitutive expression of RORgamma t by human memory Tregs suggest that, in addition to their well-known suppressive functions, these cells likely play additional, as yet undescribed, proinflammatory functions.