We present an unusual case of diffuse large B-cell lymphoma which initially presented as tension chylothorax. A 24-year-old man was admitted to our clinic with the complaints of dyspnea, fever, and sweating. Chest X-ray revealed a massive right pleural effusion. The patient was diagnosed with chylothorax and a right tube thoracostomy was performed. Thorax computed tomography revealed parenchymal infiltration in the right lower lobe, right hydropneumothorax, and multiple paratracheal lymphadenopathies. The general status of the patient was poor, and the submandibular lymph node was excised for pathological diagnosis. The general status of the patient gradually got worse and on the 13(th) day of the admission, intubation and mechanical ventilation were instituted. The pathological diagnosis of the lymph node was reported as diffuse large B-cell lymphoma, and the patient died only two days after the histopathological diagnosis. Chylothorax may arise as a complication of lymphoma. While, there are no reports on the frequency of this occurrence, it is associated with a high mortality rate when the patient presents with tension chylothorax.