A 33-year-old male presented with right side pleural plasmacytoma with secretion of Bence Jones (BJ) protein and deposition of amyloid. The pleural effusion contained a prominent peak of kappa-type BJ protein on the background of polyclonal gammopathy. Pleural biopsy disclosed features of plasmacytoma with amyloid deposition. A small peak of BJ protein was also present in serum electrophoretogram on the background of increased polyclonal IgG and IgA. Kidney function was impaired and urine protein ranged from 7.8 to 19.1 g/day with 92.5% bimodal BJ protein. There were no bone lesions by systemic bone survey, and repeated bone biopsies and marrow aspirations showed plasma cells of less than 5%. The clinical course worsened progressively; over the next five months the pleurisy became bilateral and peritoneal involvement supervened. This is believed to be the first report of primary plasmacytoma involving successively pleurae and peritoneum.