Tumor angiogenesis has been found to have prognostic significance in many tumor types for predicting an increased risk of metastasis. We assessed tumor vascularity in 28 cases of borderline malignancy and 71 cases of carcinoma of the ovary which had been resected and diagnosed, using the highly specific endothelial cell marker CD34. The numbers of microvessels were counted in 200 magnification in three highly vascularised areas. The numbers of microvessels in carcinomas were higher than that in the borderline malignancy of serous and mucinous tumors. The number of microvessels of mucinous carcinomas was significantly higher than that of serous carcinomas. There were neither significant differences in the number of microvessels according to histological tumor types (p=0.075) nor significant differences in the number of microvessels according to FIGO stages (p=0.072). But in serous carcinomas, the number of microvessels was higher in the FIGO III-IV stage than in the FIGO I-II stage (p=0.017). This study showed higher neovascularization in malignant tumor than borderline malignancy, and in the advanced stage (FIGO III-IV) than less advanced stage (FIGO I-II) of serous carcinomas.