Plasmacytoma primarily involves the bone marrow, but can also be present in many other organs. Pleural effusion in patients with multiple myeloma is not common, and has many etiologies, including congestive heart failure, nephrotic syndrome, infection, chronic renal failure, pulmonary embolism, and even secondary malignancy. Myelomatous pleural effusions in patients with extramedullary plasmacytoma are extremely rare. We presented a case of extramedullary plasmacytoma of the chest wall presenting with myelomatous pleural effusion. The myelomatous pleural effusion was diagnosed by cytology of the pleural effusion and pleural biopsy.