A 76-year-old man with silicosis was admitted to our hospital because of fever and cough. Two months prior to the admission, he had been diagnosed with pneumonia in the right upper lobe and had received antibacterial drugs at a nearby hospital. However, he had then experienced a recurrence of pneumonia and computed tomography (CT) scans had shown a nodular shadow in the anterior mediastinum which gradually increased. He was therefore referred to our hospital for further examinations. CT showed obstructive pneumonia in the right upper lobe, lymphadenopathy invading the left main bronchus, and an anterior mediastinal mass. Bronchoscopic examination revealed that the right B¹ bronchus was totally occluded by a tumor, and the bronchial lumen was narrowed by the mass from the left main bronchus to the upper left lobe bronchus. Histopathological examination revealed proliferation of lymphocyte precursor-like large lymphocytes. Immunohistochemically, these cells expressed CD138, high Ki-67 labeling indexes, and λ-dominant light chain restriction, and were negative for CD20, CD3, CD5, and CD10. Thus, he was diagnosed with plasmablastic lymphoma. Similar cells were detected on CT-guided anterior mediastinal tumor biopsy. CT showed tumor shrinkage after two cycles of combination chemotherapy consisting of etoposide, prednisolone, vincristine, cyclophosphamide, and doxorubicin, and bronchoscopy showed a marked improvement. We report a rare case of plasmablastic lymphoma with intrathoracic lesions.