Case 1 was a 62-year-old man who had performance status (PS) of 1 and stage IIIB adenocarcinoma of the lung. Because he showed progressive disease after induction chemoradiotherapy, he started to receive best supportive care alone. Three months after initial diagnosis, he complained of abdominal pain. As a result of computed tomography of the abdomen. He was diagnosed with abdominal pain probably caused by ileal perforation. An operation was undertaken and the surgical findings showed perforation by small intestine metastasis from lung adenocarcinoma. After the operation, he survived more than ten months. Case 2 was a 54-year-old man who had a PS of 3 and stage IV large cell carcinoma. After chemotherapy and sequential cranial radiotherapy, he developed anemia of unknown cause. He also complained of an abdominal pain during hospitalization and digestive tract perforation was diagnosed by a CT scan of the abdomen. He underwent surgery and the surgical findings showed a metastasis of large cell carcinoma in the small intestine. He died in a hospice two months after the operation. In the Japanese literature from 1983 to 2006. 48 operated cases with perforation caused by small intestine metastasis of lung cancer have been reported in full-length papers. Although the postoperative median survival time was 48 days, only one surgery-related death occurred. Patients who had a history of prior cancer treatment before surgery tended to achieve more prolonged survival compared to those who had not cancer treatment, probably due to poor PS. The preoperative PS may be one important prognostic factor in these patients.