Abstract: Among malignant tumors associated with chronic tuberculous pyothorax, malignant lymphoma is called pyothorax-associated lymphoma (PAL). Since the first report by Shiohara, et al. in 1970, there have been many reports of PAL, with a particularly high incidence in Japan. Involvement of Epstein Barr virus (EBV) in the disease is also suspected. Here we investigated five patients we experienced during the past 17 years from 1986 to 2002 who were diagnosed as having malignant lymphoma of thoracic origin secondary to pyothorax. Patients were four males and one female, all of whom had history of tuberculosis and artificial pneumothorax, and developed PAL after a median period of 49 years. The disease type was non-Hodgkin's B cell lymphoma in all patients. Immunostaining of histopathological specimens from all patients showed that 4 patients were positive for EB virus nuclear antigen 2 (EBNA2) and 2 for latent membrane protein 1 (LMP1). In Japan, artificial pneumothorax was performed more actively than in the United States and Europe as a therapeutic procedure for tuberculosis which was regarded as a national affliction. Onset of PAL appears to be under a strong influence of such treatment, and therefore should be predictable. Thus, those with a history of tuberculosis or pyothorax should be monitored over a long period of time.