BACKGROUND: Nearly 10% of cancer patients will develop a second primary cancer within ten years after surgical removal of the primary tumor. The detection of risk factors for developing multiple primary tumors would be important. This study was conducted to evaluate the clinical characteristics and abnormal p53 expression of lung cancer associated with multiple primary cancer(MPC). METHOD: Clinical characteristics and abnormal p53 expression were compared between 20 cases of lung cancer(NSCLC; 16 cases, SCLC; 4 cases) associated with MPC and 26 cases of primary non-small cell lung cancer. RESULT: MPC associated with lung cancer was gastric cancer(8), lung cancer(2), esophageal cancer(2), colon cancer(2), laryngeal cancer(1), bladder cancer(1), small bowel cancer(1), adrenal cancer(1), hepatocellular carcinoma(1), and breast cancer(1), in order. The clinical stage of primary NSCLC was relatively advanced, but NSCLC associated with MPC was even distribution at each stage. The detected incidences of abnormal p53 expressions were 62.5% in NSCLC associated with MPC and 76.9% in primary NSCLC(p>0.05). CONCLUSION: There was no difference in abnormal p53 expression between non-small cell carcinoma associated with multiple primary cancer and primary non-small cell carcinoma.