Dendritic cells are considered the most influential antigen presenting cells in the body because of their unique role in initiating immunity against threatening antigens. Recent studies addressing the consequences of self-antigen presentation by dendritic cells revealed the unexpected ability of these antigen presenting cells to inhibit T cell-mediated autoimmune diseases. The specific mechanisms by which dendritic cells suppress immune responses have been explored during the past year. These efforts indicate that extrathymic dendritic cells control autoimmunity by inducing peripheral T cell tolerance, a function intimately linked to their state of maturation.