To determine whether tumor angiogenesis correlates with prognosis and metastasis of patients with gastric carcinoma, we counted the microvessels within the primary carcinoma and compared their numbers with the patient's prognosis and mode of metastasis. Tumor specimens from 110 patients with gastric carcinoma, who had undergone curative resection more than 24 months before, were investigated. Intratumoral microvessels were stained with anti-CD34 and anti-von Willebrand factor monoclonal antibodies before being quantitated by light microscopy (x200). The antibody against von Willebrand factor often showed variability and stromal background staining, providing misleading low vessel counts. The data from three patients who died from nongastric carcinoma within 24 months after surgery were deleted. A total of 107 patients took part in the analysis examining the association between intratumoral microvessels and clinical outcomes. Vessel counts derived from CD34 expression were significantly higher in patients who experienced hematogenous or peritoneal metastasis after surgery than in patients with nonmetastatic tumors. No correlation between vessel counts and lymph node metastasis was found. The prevalence of hematogenous metastasis. but not peritoneal metastasis, increased as the vessel counts increased. Multivariate logistic regression and Cox hazards model analyses showed that the vessel counts obtained with CD34 staining correlated with the development of hematogenous recurrence but not peritoneal recurrence. It was the most important factor for predicting overall survival. These findings support the hypothesis that tumor angiogenesis is closely related to the development of hematogenous metastasis in human gastric carcinomas. Assessment of tumor vascularization may, therefore, prove valuable in identifying patients with gastric carcinoma at high risk for recurrence who would benefit from adjuvant therapy.