Dendritic cells (DCs) are potent antigen-presenting cells that help orchestrate the innate and adaptive immune systems to induce tolerance and immunity. They are diversified in their phenotypes, stages of maturation, degrees of activation, and functions. Several subtypes of DCs exist among human lymphoid tissues, non-lymphoid tissues, and in peripheral blood. In the skin, three types of DCs are described: Langerhans cells (LCs), dermal dendritic cells (DDCs), and plasmacytoid dendritic cells (pDCs). In the peripheral blood, myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells are well described. Dysfunctional DCs are found in many autoimmune disorders, allergies, and cancers. In this paper, we focus on DCs as related to cutaneous T cell lymphomas (CTCLs). Abnormal DC number and defective DC function are found in the blood of patients with advanced stage Sézary syndrome (SS), a leukemic variant of CTCLs. Extracorporeal photopheresis (ECP), an effective therapy for erythrodermic CTCLs, is thought to work by inducing apoptosis of tumor cells and monocytes-derived DCs. DC vaccination has been carried out successfully in some patients with CTCLs when combined with immune modifiers like toll like receptor agonists, which may enhance the function of DCs. However, DCs may perform a dual role in the pathogenesis of CTCLs. Immature DCs (langerhans cells) could promote the survival of malignant T cells. Further understanding of DCs and their role in CTCLs can help us to uncover the pathogenesis of this disease and to further explore the therapeutic uses of DCs.