BACKGROUND Myelomatous pleural effusion (MPE) is a rare occurrence in patients with multiple myeloma (MM). Fewer than 20 cases of MPE have been reported as an initial manifestation of MM. Extramedullary plasmacytoma (EMP) occurs in fewer than 5% patients with MM, and mediastinal EMP is even rarer, with only about 80 cases reported in the literature. We present a case study involving a patient with concurrent MPE and mediastinal EMP as an initial manifestation of MM. CASE REPORT The patient was a 74-year-old nonsmoking female with a 3-month history of exertional dyspnea and back pain. On exam, the patient was afebrile (temperature 37.2°C), blood pressure was 160/74 mm Hg, heart rate was 92 bpm, respiratory rate was 22/min, and oxygen saturation was 87% on room air. Patient was in mild distress and had decreased breath sounds over right lung fields about halfway up with dullness to percussion. Computed tomography of the chest showed a moderate-sized right pleural effusion and an anterior mediastinal mass. Thoracentesis showed a lymphocyte-predominant exudate. Cytology showed numerous plasma cells including immature forms. Stains for CD138 were positive, confirming plasma cell origin of cells. The anterior mediastinal mass was also biopsied and showed diffuse infiltrate of lymphocytes with plasma cell features that were also positive for CD138. Systemic protein electrophoresis showed a monoclonal immunoglobulin G kappa spike, and bone marrow biopsy was consistent with MM. CONCLUSIONS MPE and EMP are extremely rare manifestations in MM. In addition, it is extremely rare for these to be the presenting features of MM. We report concurrently occurring MPE and EMP in a patient as her initial manifestation of MM.