Plasma cell myeloma (PCM) is a hematologic malignancy of plasma cell origin and usually associated with the presence of lytic bone lesions. Pleural effusions are rarely associated with PCM and most often signify a concurrent disease process. Malignant myelomatous pleural effusions are even more unusual and carry a poor prognosis. We report a unique case of unsuspected PCM with thoracic involvement in the form of massive left side pleural effusion. Pleural fluid cytology revealed numerous atypical plasma cells. Subsequently on further workup, urine Bence Jones protein was positive. Bone marrow aspiration and biopsy and computed tomography of the chest and abdomen revealed features consistent with multiple myeloma.