A 66-year-old man, with a past history of artificial pneumothorax for pulmonary tuberculosis at the age of 17, was admitted to our hospital because of progressive left precordial pain and left anterior chest wall tumor. Because of chronic pyothorax complicated by a tumor suggested by imaging diagnosis, surgery was performed for the purpose of fenestration. A diagnosis of diffuse large cell T-cell malignant lymphoma was made by the biopsy taken at surgery. Postoperatively the patient received 6 courses of combination chemotherapy with CHOP, the course turned favorable. The left precordial pain and tumor disappeared. The patient is doing well at 11 months postoperatively. Recently, cases of malignant lymphoma developing in the chest wall of chronic pyothorax have been increased and the majority of cases of the malignant lymphoma is B-cell type. T-cell type is rare. Follow-up of chronic pyothorax's patients necessarily are attentioned on the developing of the malignant lymphoma.