We herein report an extremely rare case of a patient with IgD-lambda positive multiple myeloma presenting with myelomatous pleural effusion and ascites. A 58-year-old man visited our hospital with dyspnea as his initial symptom. His chest radiograph findings on admission revealed a left pleural effusion, and later, bilateral involvement. Computed tomography (CT) of the chest showed a paraspinal tumor with extension from the upper mediastinum to the abdomen. The cytological examination demonstrated myeloma cells in the pleural effusion and ascites, and histologically, in the pleura, an abdominal subcutaneous tumor and bone was observed. The pleural effusion was an exudate and slightly bloody. The ADA was 70 IU/L. Pleural effusion accompanying myeloma or primary pleural myeloma is very rare and, furthermore, the extremely rare findings of both myeloma cells in the ascites (although the ascites was mainly caused by liver cirrhosis) and a high ADA activity in the pleural fluid were also observed in this case.