Pneumonia and sepsis during neutropenia are common complications from chemotherapy and they are sometimes lethal. Radiation pneumonitis is also a common toxicity after thoracic radiotherapy, and severe pneumonitis causes hypoxia and death. However, the incidence and risk factors of treatment-related death from the treatment of advanced cancer using chemotherapy and/or thoracic radiotherapy are not well understood. Between July 1992 and December 1997, 1799 patients were diagnosed as having lung cancer and 784 of 1799 patients received chemotherapy in the National Cancer Center Hospital East. Of 784 patients, 18 (2.3%) died from toxicity of the initial chemotherapy. In the Japan Clinical Oncology Group (JCOG) trials for lung cancer, 29 of 1176 patients (2.5%) were reported to have died from toxicity of the treatments. Several papers have reported the risk factors of early death after chemotherapy or treatment-related death caused by chemotherapy in patients with cancer. Only poor performance status was a vigorous risk factor. Reported mortality rates of radiation pneumonitis range from 0 to 9.9% from 7 reports and 29 of 1244 patients (2.3%) died of pneumonitis after thoracic radiotherapy or chemoradiotherapy. Our previous report suggested that pulmonary fibrosis identified on plain chest X-ray film is a very strong risk factor of treatment-related death from radiation pneumonitis. At least 1-2% mortality should be expected for chemotherapy and thoracic radiotherapy. And in patients with poor PS, the expected mortality rate from chemotherapy is increased.