It has long been postulated that angiogenesis plays important roles in tumor cell proliferation and hormonal secretion of endocrine tumors, including adrenocortical neoplasms. Detailed examination of vascularity, however, has not been reported in adrenocortical tumors. In this study, we quantitatively examined vascularity in normal adrenal, adrenocortical adenoma, and carcinoma using an image analysis system to evaluate vascularity or angiogenesis in these lesions. Vascular density (VD: vessel number/mm2), endothelial area of each vessel (EA: microm2/vessel) and vascular area (VA: the percentage of EA per field) were examined using immunohistochemical analysis of CD34 and the CAS 200 image analysis system. EA and VA of adrenocortical carcinomas (EA, 113.4 +/- 33.1; VA, 6.34 +/- 2.03) were significantly higher than those of adenoma (EA, 66.1 +/- 43.0; VA, 3.11 +/- 1.56) and normal adrenal tissue (EA, 65.4 +/- 26.0; VA, 4.26 +/- 1.19). There were no significant differences in VD among normal cases (702.2 +/- 173.2), adenomas (488.9 +/- 153.2), and carcinomas (573.2 +/- 185.2). These results suggest that adrenocortical carcinoma might be associated with increased endothelial cell proliferation but not with an increased number of intratumoral microvessels. There were no significant differences in these parameters of vascularity examined in the zona glomerulosa, zona fasciculata, and zona reticularis of aldosteronomas, Cushing's adenomas, and nonfunctioning hormonally inactive adenomas nor between specimens from patients who died of the disease and those from patients who did not.