A 78-year-old man was referred to our hospital for fever and fatigue. Chest computed tomography (CT) scan revealed ground-glass opacity, predominantly in both upper lobes, and a mass shadow in the left lower lobe. He was given a tentative diagnosis of infection but although he received antibiotics, his fever did not improve. We performed a transbronchial lung biopsy; however, we did not obtain meaningful diagnostic findings. On his ninth day in the hospital, he was administered methylprednisolone pulse therapy because of respiratory failure and his condition improved. A CT scan was performed again on the 21st day of admission and showed para-aortic lymph node enlargement, a left adrenal grand mass, and increased retroperitoneal fatty tissue density. To obtain a definitive diagnosis, we performed CT-guided needle biopsy on the mass shadow in the left lower lobe. The histopathological findings revealed diffuse large B-cell lymphoma. The patient was therefore scheduled to be transferred to a hospital specializing in hematological diseases, but he died on the 30th day of admission. An autopsy revealed that the malignant lymphoma had infiltrated multiple organs. In cases of abnormal lung findings refractory to antibiotics, it is important to consider malignant lymphoma as a differential diagnosis.