Serum tumor markers are non-invasive diagnostic tools for malignant tumor and commonly used for screening of cancer and as an indicator of treatment-effect. In small cell lung cancer, NSE and proGRP are effective markers. In non-small cell lung cancer (NSCLC), CEA, SCC, CYFRA21-1, SLX and CA19-9 are commonly used for screening, and at least one marker among CEA, SCC or CYFRA21-1 is positive in 77% of patients with NSCLC. According to the histological type, the positive rate of CEA and CYFRA21-1 is high in adenocarcinoma patients, and the positive rate of CYFRA21-1 and SCC is high in squamous cell carcinoma patients. This review summarizes the clinical usefulness of tumor markers in primary lung cancer.