After chemotherapy and radiotherapy for non-Hodgkin's lymphoma during a one-year period, a 66-year-old man developed synchronous triple lung cancers in both lungs. Of the three resected tumors, one was advanced large cell carcinoma with neuroendocrine morphology, and the other two were early squamous cell carcinoma without lymph node metastasis. Although he received repeated chemotherapy for lung cancer, the patient died of hepatic failure due to multiple liver metastases. Autopsy revealed disseminated metastasis of the large cell carcinoma with neuroendocrine morphology throughout the entire body, but no recurrence of malignant lymphoma or squamous cell carcinoma was found. To our knowledge, this is the first report of triple lung cancers occurring after treatment for malignant lymphoma.