A 73-year-old woman visited our hospital with chief complaint of dyspnea. She had been diagnosed as marginal zone B cell lymphoma of the mucosa-associated lymphoid tissue type by parotid gland tumor biopsy two years earlier. Chest computed tomography on admission showed infiltrates resembling cardiogenic pulmonary edema and bilateral pleural effusion. An 18-fluorodeoxyglucose-positron emission tomography/computed tomography revealed standard uptake value of 3.71 to 17.02 in bilateral neck lymph nodes, bilateral lung fields, the pancreas head, the right kidney, the left urinary tract, and the lymph nodes near the urinary tract. While bronchoscopic examination and thoracentesis showed no malignancy, biopsy of subcutaneous nodule under the left ear led to the definitive diagnosis of diffuse large B cell lymphoma. After chemotherapy was started, pulmonary infiltrates and pleural effusion diminished. Complete remission was attained after 6 cycles of chemotherapy.