Angiogenesis generally plays an essential role in tumor growth and metastasis, and also influences the response to treatment in human malignant solid tumors. Even in nonmalignant tumors, angiogenesis is essential for tumor growth and invasion. In order to define the relationship between tumor vascularity and the clinical course in patients with pituitary adenomas, we quantified the vascularity in 47 pituitary adenomas and in 6 normal anterior pituitary glands obtained at autopsy using a computed image-analyzing system. We estimated two parameters, the vascular number and the area as the vascularity. Additionally, we calculated mean individual vessel size using the above two parameters. The relationships of tumor vascularity to clinical, endocrinological and histological findings was assessed. Factors considered included patient age and gender, preoperative medication, histological type, concentration of each hypersecreted pituitary hormone, maximum tumor size, cavernous sinus invasion, intratumoral hemorrhage, and immunohistological results of localization of vascular endothelial growth factor (VEGF). Vascularity was significantly higher in normal glands than in pituitary adenomas. However, there were no significant correlations between tumor vascularity and other clinical, endocrinological, or histological parameters, suggesting that increased angiogenesis is not essential for pituitary adenoma growth or invasiveness.