The well-known prognostic factors for breast cancer, such as axillary lymph node status, do not always account for the exact outcome. The development of other accurate prognostic factors would help in assessing high risk for recurrence and death. Recently, much experimental evidence has accumulated showing that tumor growth and metastasis are dependent on tumor angiogenesis. To investigate the status of angiogenesis in breast cancer, we counted the microvessel density (MVD) of breast cancer tissues, which were stained with anti-CD34 antibody, as a measure of tumor angiogenesis. We classified 43 breast-cancer patients into 22 with low MVD (<47/200xPF) and 21 with high MVD (≥47/200xPF). We estimated the correlations between the MVD and other established prognostic factors. We also calculated survivals based on MVD. The MVD was in the range between 10 and 93 (mean±SD=46.9±21.7). The positive rate of lymph-node metastasis in high-MVD patients was 32.6%, which was higher than the 23,3% for low-MVD patients. We found a significant correlation between MVD and histologic grade (p=0.037), but could not find any significant correlation between MVD and menopausal status, tumor size, nuclear grade, estrogen receptor, or progesterone receptor. Retrospectively, the receptor status of estrogen and of progesterone had significant impacts on survival (ER: p=0.0001, PR: p=0.0001). The 4-year disease-free survival rate of high-MVD patients was 56.6±12,5%, and that of low-MVD patients was 69.0±10.8% (p=0.449). The 4-year overall survival rate of high-MVD patients was 71.1±11.1%, and that of low-MVD patients was 74.1±12.2 (p=0,449). In conclusion, the determination of MVD in breast cancer tissue may be useful as a prognostic factor, but it is necessary to investigate the MVD in a large number of patients before this conclusion can be stated with certainty.