Prognostic factors of patients with metastatic lung tumors were evaluated on 72 patients who were treated with pulmonary resection (49 via lateral thoracotomy and 23 via median sternotomy). The 5-year survival rate of these patients was 41.3%. Two factors, i.e., tumor free interval (TFI) and tumor size, significantly affected the survival after surgery. Patients with a longer TFI and smaller tumor(s) were associated with a favorable prognosis. The prognosis, however, was neither affected by the number of metastatic lung tumors nor whether they were unilateral or bilateral. The prognosis of lung metastases from colorectal cancer was the most favorable (61.4% at 5-year). On the other hand, patients with lung metastases from renal cell carcinoma and breast carcinoma showed poor prognosis respectively. As for testicular tumors and bone or soft tissue sarcomas, chemo-sensitivity is the most important prognostic factor. Good responders to prior chemotherapy showed a better prognosis than poor responders. These results urge the reappraisal of the role of surgery in the treatment of metastatic lung tumors and demonstrate that aggressive surgery can be indicated even for multiple or bilateral lung metastases. Nature of metastatic tumors, i.e., their origin and chemo-sensitivity, must be taken into consideration when the indication for surgery is decided.