Abstract: Multiple myeloma is a common hematological malignancy. Serous effusions are described uncommonly in myelomas. A myelomatous effusion however, is extremely rare and carries a poor prognosis. We report a case of multiple myeloma with leukemic transformation and simultaneous pleural fluid involvement in a 66-year old patient who was receiving chemotherapy. The patient developed exceptional dyspnea, dry cough and fatigue prior to admission. Radiological investigations revealed a massive pleural effusion with partial collapse of the lung. Pathological examination of the fluid showed plasma cells and plasmablasts with abnormal forms, consistent with a myelomatous pleural effusion. Hematopoietic neoplasms are associated with body cavity effusions but rare etiologies such as myeloma should also be considered as the treatment protocols differ in these cases.