Among all cases of surgically resected lung cancer, there were 56 cases (16.1%) of double primary cancer. The common sites of the other primary cancer was the stomach (19 cases), followed by large intestine (9 cases), urinary bladder (7 cases) and pharinx-larynx (7 cases). One patient had triple cancers. In all cases of double primary cancer, 46 cases were metachronous, 10 of which were cases of initial lung cancer. The 5-year survival rate of double primary cancer was 39.7%. Good result was obtained in metachronous cases with initial lung cancer. Most of prognosis of double primary cancer was determined by that of lung cancer. In more than half of initial cancer, the second primary cancer was detected by symptoms. So, special attention to the possibility of double primary cancer in patients with resected lung cancer is necessary for improvement of prognosis.