Waldenström macroglobulinemia is a lymphoplasmacytic lymphoma characterized by production of the immunoglobulin M (IgM) monoclonal protein. Commonly involved sites are the bone marrow, lymph nodes, and spleen. Lymphoplasmacytic infiltration of the central nervous system (CNS), in contrast, is referred to as Bing-Neel syndrome, and is an extremely rare phenomenon. Here, we present a unique case of Waldenström macroglobulinemia with optic neuritis accompanied by monoclonal expansion of T cells, which recovered after administration of CNS-targeting chemotherapy. Although the underlying causal relationships in this case remain obscure, aberrantly expanded T cells may have contributed to the development of optic neuritis, and we should be reminded that some types of cranial neuropathy in Waldenström macroglobulinemia may be reversible.