A case with primary plasmacytoma of the lung is described. The patient, a 55-year-old Japanese female, who simultaneously had a pulmonary plasmacytoma and bladder carcinoma. The bladder tumor was treated with transurethral resection. Pathologically, the bladder tumor was a non-invasive, papillary transitional cell carcinoma, grade II. The lung tumor was located in the right upper lobe and upper lobectomy was performed. The tumor measured 2.8 x 2.7 x 2.0 cm and had a white-yellowish cut surface. Histologic, electron microscopic and immunohistochemical examinations of the lung tumor revealed monoclonal proliferation of plasma cells (IgA, lambda light chain). There was no evidence of multiple myeloma.