BACKGROUND AND OBJECTIVE The importance of accurate staging according to the international TNM staging system of non-small cell lung cancer (NSCLC) for patient management and ascertaining individual prognosis cannot be overemphasized. The TNM classification is scheduled to be revised in 2007. In a large single-center collective we investigated the prognosis for patients who had complete resection of a NSCLC. PATIENTS AND METHODS We retrospectively reviewed hospital records and follow-up data of 2,378 patients operated on between 1996 and 2005 for NSCLC. Complete resection was achieved in 2,083 patients. Systematic hilar and mediastinal lymph node dissection was performed concurrently. Probability of survival was then analysed with the Kaplan-Meier method. The significance of differences between subgroups was calculated using the log-rank test. Odds ratios with 95 % confidence intervals (CI) were calculated for each characteristic. The Cox model was used for multivariate analyses. RESULTS The 5-year survival for patients after complete resection was 50.7 %. The 5-year survival rates for clinical stages were 72 % for stage IA, 59.8 % for stage IB, not defined for stage IIA, 47,8 % for stage IIB, 45 % for stage IIIA, 38.7 % for stage IIIB, and not defined for stage IV. There were significant differences in survival between stages IIIB and IV (p = 0.013). There was a trend towards significance between patients with IA and IB (p = 0.052). However, there was no significant difference between patients with all the other stages. 5-year survival according to pathological stages was: stage IA 68.5 %; stage IB 66.6 %; stage IIA 55.3 %; stage IIB 49.0 %; stage IIIA 35.8 %; stage IIIB 35.4 %; stage IV not defined. Gender, age and type of histology were found by multivariate analysis to be significant independent prognostic factors for survival. CONCLUSIONS The TNM and stage grouping classification is valid for defining prognosis and prognosis-related criteria in patients with NSCLC. The difference in prognosis between clinical stages IIIB and IV was significant, but not that between all the other related subgroups. Concordance with histological staging demonstrated the quality of existing clinical staging methods and related strategies. Complete surgical resection, age, gender, histology and stage of the disease significantly influenced long-term survival.