Elevated cytokines in bone marrow (BM) micro-environment (interleukin-6 [IL-6], transforming growth factor-beta [TGF-β], and IL-1β) may play an important role in observed immune dysfunction in multiple myeloma (MM). As IL-6 and TGF-β are important for the generation of T-helper 17 (T_H17) cells, we evaluated and observed a significantly elevated baseline and induced frequency of T_h17 cells in peripheral blood mononuclear cells (PBMCs) and BM mononuclear cells (BMMCs) from MM patients compared with healthy donors. We observed significant increase in levels of serum IL-17, IL-21, IL-22, and IL-23 in blood and BM in MM compared with healthy donors. We also observed that myeloma PBMCs after T_H17 polarization significantly induced IL-1α, IL-13, IL-17, and IL-23 production compared with healthy donor PBMCs. We next observed that IL-17 promotes myeloma cell growth and colony formation via IL-17 receptor, adhesion to bone marrow stromal cells (BMSCs) as well as increased growth in vivo in murine xenograft model of human MM. Additionally, we have observed that combination of IL-17 and IL-22 significantly inhibited the production of T_H1-mediated cytokines, including interferon-γ (IFN-γ), by healthy donor PBMCs. In conclusion, IL-17–producing T_h17 cells play an important role in MM pathobiology and may be an important therapeutic target for anti-MM activity and to improve immune function.