PURPOSE: To investigate the impact of the proposed International Association for the Study of Lung Cancer (IASLC) tumor, node, metastasis (TNM) system on staging and outcome of non small cell lung cancer (NSCLC). MATERIALS AND METHODS: With a total of 501 NSCLC patients with staging according to Union for International Cancer Control (UICC), 6th TNM (TNM-6) were reclassified according to the IASLC proposed TNM staging (TNM-7). The impact of TNM-7 in comparison with TNM-6 was evaluated at three levels: change in substage, staging, and outcome. The outcome measure was to compare the stage-specific overall survival of NSCLC between the two groups of patients. RESULTS: A total of 214 (42.7%) patients had changed TNM staging, and 101 (20.2%) patients had changed stage groupings in TNM-7 compared to TNM-6. Among 100 patients showing changed stage grouping, 72 (14.4%) showed upstage and 29 (5.8%) demonstrated downstage. The TNM-7 system resulted in better separation of survival curves among stage-specific NSCLC than TNM-6 system, especially in separation of stage IIA vs. IIB (p = 0.023) and stage IIIB vs. IV (p < 0.001). CONCLUSION: TNM-7 for lung cancer appears to be superior in defining stage-specific survival groups than TNM-6, especially between stage IIA vs. stage IIB and stage IIIB vs. stage IV.