CD4 T cells play a major role in the development and persistence of autoimmune rheumatic diseases. The recent identification of IL-17-producing Th17 cells as a potent proinflammatory subset extends the understanding of pathophysiological processes not explained by the Th1/Th2 dichotomy. The recent data from human studies discussed in this article indicate an important pathogenic function for Th17 cells and Th17-derived IL-17 suggesting that therapies targeting Th17 cells/IL-17 may be of potential use in the treatment of those diseases.