The authors investigated the relationship between hemorrhage and the expression of vascular endothelial growth factor (VEGF) in pituitary adenomas. The subjects were 39 patients with pituitary adenomas. Surgically obtained tumor tissue was immunohistochemically stained using antibodies against VEGF, CD-34, Ki-67, and anterior pituitary hormones. The expression of VEGF was graded as 0, 1+, and 2+. The relationship between intratumoral hemorrhage and factors such as tumor size, Ki-67 labeling indices, number of CD-34 positive vessels, and VEGF expression was examined by multivariate analysis. High-grade VEGF expression was the sole independent factor correlated with intratumoral hemorrhage. The number of CD-34 positive vessels had no effect on the incidence of hemorrhage in patients with pituitary adenomas. In conclusion, a positive relationship between VEGF expression and hemorrhage in pituitary adenoma was observed. The patho-mechanical significance of this correlation is under investigation.