Microvessel density (MVD) is regarded as a surrogate marker for angiogenesis and has been used for tumor prognosis. In this study, MVD was identified immunohistochemically by monoclonal antibodies against CD105 and CD34 in the tissues representing gastric carcinoma, chronic gastritis, and hyperplastic polyps, and the results were correlated with clinicopathologic features. The expression of CD105 in the microvessels within benign lesions was barely visible, and MVD was markedly lower than that determined by CD34. CD34 was strongly expressed in the microvessels within hyperplastic polyps and tissues with gastritis. In gastric carcinoma, CD105 expression in microvessels was as high as the MVD, compared with benign lesions. CD105 stained well-formed mature and newly formed immature vessels within the cancer mass. Correlation analysis showed that MVD determined by CD105 correlated with blood vessel invasion, distant metastasis, and formation of ascites. Survival analysis demonstrated an inverse correlation between MVD count and overall survival: patients with MVD counts of 32 or higher survived for a much shorter time than those with counts lower than 32. Multivariate analysis confirmed that MVD determined by CD105 was an independent prognostic factor for survival. Microvessel density determined by CD34 inversely correlated with overall survival, but it did not correlate with other clinicopathologic parameters except formation of ascites. In conclusion, CD34 was universally expressed in blood vessels within benign and malignant tissues, whereas CD105 expression was minimal in benign tissues but stronger in gastric carcinoma. These data suggest that both CD105 and CD34 could be used for quantification of angiogenesis, but preference should be given to CD105 in the evaluation of prognosis in gastric carcinoma.