BACKGROUND: Accurate staging is important to determine treatment modalities and to predict prognosis for the patients with lung cancer. The simple two-stage system of the Veteran's Administration Lung Cancer study Group has been used for staging of small cell lung cancer(SCLC) because treatment usually consists of chemotherapy with or without radiotherapy. However, this system does not accurately reflect segregation of patients into homogenous prognostic groups. Therefore, a variety of new staging system have been proposed as more intensive treatments including either intensive radiotherapy or surgery enter clinical trials. We evaluate the prognostic importance of TNM staging, which has the advantage of providing a uniform detailed classification of tumor spread, in patients with SCLC. METHODS: The medical records of 166 patients diagnosed with SCLC between January 1989 and December 1996 were reviewed retrospectively. The influence of TNM stage on survival was analyzed in 147 patients, among 166 patients, who had complete TNM staging data. RESULTS: Three patients were classified in stage l /ll, 15 in stage llla, 78 in stage lllb and 48 in stage lV. Survival rate at 1 and 2 years for these patients were as follows stage l/ll, 75% and 37.5% ; stage llla, 46.7% and 25.0% ; stage lllb, 34.3% and 11.3% ; and stage lV, 2.6% and 0%. The 2-year survival rates for 84 patients who received chemotherapy(more than 2 cycles) with or without radiotherapy were as follows stage l/ll, 37.5% ; stage lll, 31.3% ; stage lllb 13.5% ; and stage lV 0%. Overall outcome according to TNM staging was significantly different whether or not received treatment. However, there was no significant difference between stage llla and stage lllb though median survival and 2-year survial rate were higher in stage llla than stage lllb. CONCLUSION: These results suggest that the TNM staging system may be helpful for predicting the prognosis of patients with SCLC.