Vascular endothelial growth factor (VEGF) is one of the most important factors for angiogenesis in various malignant tumors. However, the biological significance of VEGF in lung adenocarcinoma remains unclear. We stained intratumoral microvessels immunohistochemically using anti-CD34 antibody and analyzed VEGF expression using anti-VEGF antibody in 44 cases of stage I lung adenocarcinoma. Of the 44 patients studied, 14 patients had a postoperative relapse, and 30 patients did not. The mean microvessel count (MVC) in stage I lung adenocarcinoma was 79.5 +/- 26.9 per x200 microscopic field. Immunohistochemical expression of VEGF was found in 27 of 44 cases of stage I lung adenocarcinoma. The mean MVC in cases of VEGF-positive lung adenocarcinoma (86.4 +/- 28.2) was significantly higher than that in cases of VEGF-negative lung adenocarcinoma (68.6 +/- 21.4; P < 0.05). The high-MVC group patients (MVC > 80) had significantly worse survival rates than those in the low-MVC group (MVC < or = 80; P < 0.01), and patients with VEGF-negative tumors had significantly better survival rates than those with VEGF-positive tumors (P < 0.05). We conclude that angiogenesis, as assessed by intratumoral MVCs, is a significant prognostic factor in stage I lung adenocarcinoma, and that VEGF is an important angiogenic factor in stage I lung adenocarcinoma.