We present a case of pyothorax-associated T-cell lymphoma in which Epstein-Barr virus (EBV) genome is not detected in the tumor cells. An 80-year-old male came to our hospital because of a left chest pain. Chest computed tomography (CT) showed a mass at the lower-dorsal part of the pyothorax wall, which involved the adjacent chest wall. The surgical biopsy specimen showed a predominant infiltration of atypical lymphocytes. Results of immunohistochemical analysis were as follows: CD3+, CD4-, CD8+, CD20-, CD30-, CD45RO+ and CD79a-. We diagnosed this case as a type of peripheral T-cell lymphoma. In situ hybridization using EBV-encoded RNA-1 (EBER-1) did not reveal the positive signals in the nucleus of tumor cells. Polymerase chain reaction (PCR) analysis yielded a negative result for human herpesvirus 8 (HHV8). Radiation therapy at 54 Gy reduced the tumor size by 90%. Visual and hearing disturbances of unknown etiology developed just before the completion of radiotherapy. The symptoms progressively worsened and the patient became bedridden. He died of pneumonia 2 months after the completion of radiotherapy. Autopsy did not reveal abnormalities to which the neurological disturbances were attributable.