Solitary extramedullary plasmacytomas represent 3% of plasma cell neoplasms. Their most common locations are the upper gastrointestinal and respiratory tract. We report a 70-year-old male presenting with progressive dyspnea and cough. A chest radiography showed widened mediastinum. Chest computed tomography showed a mediastinal mass. A bronchoscopy showed an extrinsic compression and complete occlusion of the primary bronchus. A self-expandable prosthesis was installed in left bronchus. A population of plasmacytoid cells was evidenced in the mass biopsy. Immunohistochemistry revealed CD20+ and CD138+. These tumor cells stained positively for lambda light chains, but negatively for kappa chains. Therefore an extramedullary plasmacytoma was diagnosed. A multiple myeloma was discarded with a normal blood count, serum calcium and creatinine levels. Serum protein electrophoresis had a monoclonal spike, serum IgG was 1963 mg/dl. Bone marrow aspiration had 1% of plasma cells. Bone x-rays were normal. Computed tomographies of the neck, thorax, abdomen and pelvis ruled out other plasmacytomas. Eight cycles of chemotherapy with thalidomide, melphalan and prednisone were indicated, obtaining complete remission of the tumor. The review of the literature shows that mediastinal extramedullary plasmacytomas are extremely rare. They generally appear in men aged between 50 and 60 years. The treatment of choice is radiotherapy, but given the location in the present case, chemotherapy was considered the best option. Recurrence is approximately 10 to 30% and 10% of patients progress to myeloma, thus requiring close monitoring.