A-59-year old man was admitted to the hospital with a 2-month history of the right pleuritic chest discomfort and mild dyspnea. Seven years earlier, he was operated on left pneumonectomy for squamous cell carcinoma of left upper lobe (Stage IIb, T₂N₁M₀). The computed tomographic scan revealed an anterior herniation of the right lung in the left hemithorax. A single thorax after receiving pneumonectomy is called a "buffalo chest" because the absence of an anatomical separation of the two hemithoraxes resembles that of the North American buffalo or bison. A possible pneumothorax should be catastrophic for the patient, so he should be closely monitored regarding any invasive procedure or trauma. He improved after symptomatic treatment.