Of 908 patients who underwent operation for primary lung cancer between January 1985 and June 1996, we considered 57 (6.3%) to have a second primary lung cancer, which was synchronous in 28 cases (3.1%) and metachronous in 29 cases (3.2%). Five-year survival for patients with synchronous and metachronous disease from initial treatment of cancer was 70.3% and 66.0%, respectively. Survival after the development of a metachronous lesion was 32.9% at 5 years. Sixteen of the synchronous second tumors (57%) were detected on preoperative radiography or bronchoscopy and 11 (39%) at the time of operation. Survival of patients at stage I or II from treatment of a synchronous lesion (p = 0.002) and of a metachronous second lesion (p = 0.028) was significantly better compared with those at stage III or IV. Therefore it is important to carefully examine a synchronous lesion before and during the operation of a primary lung cancer and to perform close follow-up surveillance for early detection of a metachronous lesion. In treating multiple lung carcinomas consideration should always be given to performing precise staging, aggressive operative approach for early stage, and oncologically sound parenchymal sparing procedures.