Nodal marginal zone lymphomas are indolent and rare non-Hodgkin lymphomas, most often diagnosed at an advanced stage. Their clinical presentations are typically insidious, which can lead to delayed diagnosis. The concomitant secretion of IgM and IgG immunoglobulins with kappa light chains constitutes an exceptional feature in this type of lymphoma, as illustrated by our case. We report the case of a 62-year-old man with a history of treated syphilis and inferior vena cava thrombosis managed with rivaroxaban, who presented with a left inguinal mass evolving over three months, accompanied by fever, night sweats, and weight loss. Clinical examination revealed non-inflammatory left inguinal lymphadenopathy without other abnormalities. Laboratory tests showed non-regenerative anemia, leukopenia, and elevated LDH levels. Protein electrophoresis revealed a monoclonal peak in the gamma region, confirmed by serum immunofixation showing two monoclonal bands of IgG kappa and IgM kappa types. Biopsy of the inguinal lymph node revealed histological and immunohistochemical features consistent with a small B-cell marginal zone lymphoma, staged as IV based on the extension workup. A chemotherapy regimen consisting of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) was initiated, resulting in a partial response after four cycles. The coexpression of IgM and IgG kappa light chains in nodal marginal zone lymphomas, which are already rare, is an unusual finding. This particularity warrants multicenter studies to better assess its diagnostic, prognostic, and therapeutic implications.