Angiopoietin (Ang)-1 and -2 have been recently identified as potent angiogenic factors which function in concert with vascular endothelial growth factor (VEGF), but no detailed clinical study on Ang expression has been reported. To assess the clinical significance of Ang expression in non-small cell lung cancer (NSCLC), a total of 236 patients with pathological stage-I-IIIA disease were retrospectively reviewed. Expression of Ang-1, Ang-2, or VEGF was examined immunohistochemically; intratumoral microvessel density (IMVD) was examined with immunohistochemical staining against CD34, a marker of pan-endothelial cells (CD34-IMVD), and that against CD105, a marker of proliferative endothelial cells (CD105-IMVD). Positive expression of Ang-1 and that of Ang-2 were seen in 101 (42.8%) and 40 patients (16.9%), respectively. There was no significant correlation between Ang-1 expression and CD34-IMVD or CD105-IMVD. In contrast, the average CD105-IMVD for Ang-2-positive tumor was significantly higher than that for Ang-2-negative tumor (56.7 versus 38.5; P = 0.032). More interestingly, such an angiogenic effect of Ang-2 was seen only when VEGF expression was high; when VEGF expression was high, the average CD105-IMVD for Ang-2-positive tumor was significantly higher than that for Ang-2-negative tumor (89.1 versus 63.6; P = 0.045); when VEGF expression was low, the average CD105-IMVD for Ang-2-positive tumor and that for Ang-2-negative tumor were almost the same (27.4 and 27.1, respectively). Moreover, positive expression of Ang-2, not Ang-1, was a significant factor to predict a poor postoperative survival (5-year survival rates for Ang-2-positive patients and -negative patients were 53.5 and 70.3%, respectively; P = 0.027), which was confirmed by a multivariate analysis. The influence of Ang-2 status on postoperative survival was enhanced when VEGF expression was high. That said, the 5-year survival of Ang-2-positive and VEGF-high patients was extremely low (41.4%) as compared with that for Ang-2-negative and VEGF-low patients (66.6%), as compared with that for Ang-2-positive and VEGF-low patients (63.6%), and as compared with that for Ang-2-negative and VEGF-low patients (71.8%). In conclusion, positive Ang-2 expression was significantly correlated with a poor prognosis, as well as with aggressive angiogenesis in resected NSCLC that was enhanced in the presence of high VEGF expression.