Experimental evidence suggests that tumor growth and progression depend on angiogenesis. In a retrospective study we evaluated the relationship between tumor angiogenesis and survival in patients with NSCLC treated with potentially curative surgery between 1992 and 1997. The study population consisted of 76 patients. An anti-CD34 monoclonal antibody was used to measure angiogenesis in tumor samples. Angiogenesis was quantified in terms of microvessel count (MVC): in each sample the three most intense regions of neovascularization were identified under low microscopic power. A x250 field in each of the three areas was then counted and the highest count of the three fields was recorded. Disease free (DFS) and overall survival (OS) during follow up were evaluated. Gender, age, stage, histologic type and KI-67 were the other factors considered for analysis. The median MVC in our series was 41.5. Among the clinicopathologic parameters examined the microvessel count was the only one to show a significant association with disease free survival in univariate analysis (P = 0.04). MVC value is a new indicator of tumor aggressiveness in patients with NSCLC who underwent potentially curative surgery and should be taken into consideration in selecting patients for adjuvant treatment.