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.