Multiple myeloma (MM) is a B-cell malignancy. The monoclonal immunoglobulin, secreted by myeloma plasma cells, carries unique antigenic determinants (idiotype [Id]) that can be regarded as a tumor-specific antigen. Id-based immunotherapy has been explored in myeloma patients for the purpose of enhancing or inducing Id-specific immune responses that might lead to tumor destruction. However, despite some evidence obtained from mouse plasmacytoma models, it is still unclear whether Id-specific immunity may play a role in the regulation of tumor cells in MM. In the current study, using dendritic cells (DCs) as antigen-presenting cells, autologous Id-specific cytotoxic T lymphocyte (CTL) lines containing both CD4⁺ and CD8⁺ T cells were generated from myeloma patients. The results show that Id-specific CTLs not only recognized and lysed autologous Id-pulsed DCs but also significantly killed the autologous primary myeloma cells. The cytotoxicity against the primary tumor cells was major histocompatibility complex (MHC) class I– and, to a lesser extent, class II–restricted, indicating that myeloma cells could process Id protein and present Id peptides in the context of their surface MHC molecules. Furthermore, the CTLs lysed the target cells mainly through the perforin-mediated pathway because Concanamycin A, but not Brefeldin A—the selective inhibitors for perforin- or Fas-mediated pathways—abrogated the cytolytic activity of the cells. These CTLs secreted predominantly interferon-γ and tumor necrosis factor-α on antigen stimulation, indicating that they belong to the type-1 T-cell subsets. Taken together, these findings represent the first demonstration that Id-specific CTLs are able to lyse autologous tumor cells in MM and, thus, provide a rationale for Id-based immunotherapy in the disease.