Lung carcinoma is a common malignant disease in adults. Various genetic changes associated with small cell and non-small cell lung carcinoma are now known. There are two types of genetic change which influence tumor growth and patient prognosis. Among oncogenes, c-myc, K-ras, and erbB-2 are considered to play important roles in lung carcinogenesis. The p53 suppressor gene is highly expressed in small and non-small cell carcinoma. To differentiate between double primary lung carcinomas and intrapulmonary metastasis, or between primary lung carcinoma and metastatic lung tumor, the analysis of gene mutations, such as of p53 and K-ras, appears to be very useful.