['Therapeutic strategies remain controversial for the completely resected stage I non-small cell lung cancer patients with worse long-term survival. Comprehensive patient selection for adjuvant chemotherapy should be based on proven risk factors.', 'The records of 610 patients with pathologic stage I complete pulmonary resection were retrospectively reviewed. Survival was analyzed by the Kaplan-Meier method, log-rank test, and Cox proportional hazards analysis.', 'Overall 5-year survival rate was 75.1%. Univariate analysis for all patients revealed eight significant prognostic factors: age (p < 0.0001); gender (p = 0.0001); histopathology (p < 0.0001); differentiation (p < 0.0001); tumor size (T factor) (p < 0.0001); pleural involvement (p = 0.0007); blood vessel involvement (p < 0.0001); and lymphatic vessel involvement (p < 0.0001). Multivariate analysis revealed age, tumor size, and lymphatic vessel involvement as significant factors. Hazard ratios for death were 0.563 for age younger than 70 years (p = 0.0004), 0.629 for T1 tumor (p = 0.0126), and 0.514 for ly(-) (p = 0.0002). Five-year survival rates in patients with T1 without lymphatic vessel involvement, T1 with lymphatic vessel involvement, T2 without lymphatic vessel involvement, and T2 with lymphatic vessel involvement were 88.7, 69.8, 73.5, and 56.1%, respectively. Overlapping prognoses were seen between T1 with lymphatic vessel involvement classed as stage IA and T2 without lymphatic vessel involvement classed as stage IB disease.'] Is intratumoral lymphatic vessel involvement an invasive indicator of completely resected pathologic stage I non-small cell lung cancer?