A 45-year-old woman with rheumatic arthritis history suffered from fever and some airway symptoms. She was treated as airway infection and rheumatic arthritis flare up initially. Owing to recurrent fever, she was admitted. Chest computed tomography (CT) showed left lower lung minimal ground-glass opacities and splenomegaly. Pulmonary samples from video-assisted thoracoscopic surgery revealed diffuse large B-cell lymphoma. Because subsequent FDG-PET for staging showed a characteristic diffuse pulmonary FDG uptake pattern without corresponding CT abnormality, intravascular large B-cell lymphoma (IVLBCL) was suspected. Further pathologic review made the final diagnosis of IVLBCL, a subtype of diffuse large B-cell lymphoma.