A 52-year-old man noted large amounts of bloody sputum and visited our hospital. Chest X-ray showed a mass shadow in the right upper lung field. He was diagnosed with squamous cell carcinoma (SCC). Although he was not aware of symptoms other than the bloody sputum, his blood chemistry showed a high total serum protein level of 10.6 g/dl. Further analysis of serum immunoglobulin revealed a markedly high immunoglobulin G (IgG) level, but an abnormally low level of immunoglobulin A (IgA) and immunoglobulin M (IgM). Serum immunoelectrophoresis detected IgG-lambda monoclonal protein; therefore, we suspected the coexistence of multiple myeloma, amyloidosis, benign macroglobulinemia, or benign monoclonal gammopathy. Since the patient continued to expectorate large amounts of bloody sputum every day, and his anemia progressed, right upper lobectomy and lymph node dissection were performed on a semi-emergent basis without preoperative bone marrow examination. On thoracotomy at the level of the fifth intercostal space, the fifth and sixth ribs were partially resected posteriorly, and the resected ribs were submitted for pathological examination. The postoperative pathological diagnosis was SCC of the lung (p-T2N0M0, stage IB). Pathological examination of the ribs revealed IgG-lambda myeloma. Herein, we report a patient with lung cancer in whom multiple myeloma was definitively diagnosed from rib specimens resected at thoracotomy.