The article reports a review of 1140 cases of primary lung cancer diagnosed between 1974 and 1987 (13-year period) to examine the clinicopathologic features of multiple primary lung cancer. The following criteria were used: There were no malignant tumors in other organs; the tumors were separate or located in different lobes; the tumors were of different histologic types; if the histologic types were similar, there was no carcinoma in the common lymphatics of any tumors and no extrapulmonary metastases at the time of diagnosis. The following results were obtained: The incidence was 1.2% (14 of 1140 cases); 11 patients were heavy smokers; the most common histologic type was squamous cell carcinoma, and the combination of two squamous cell carcinomas was most common; 12 cases were bilateral, and 11 cases were synchronous; 19 tumors were diagnosed by bronchoscopic biopsy; 9 patients with bilateral tumors received chemotherapy and radiation therapy.