Angiogenesis is essential for tumor growth and metastases. Studies in breast carcinomas suggest that microvessel quantitation as a measure of angiogenesis might be one of the most powerful prognostic tools available. Node negative breast cancer is a particular group for which better prognostic markers would be helpful. We therefore measured microvessel density in a series of well characterised node negative breast carcinomas to evaluate angiogenesis as a prognostic marker and assess its relationship to epidermal growth factor receptor (EGFR) and estrogen receptor (ER), which have previously been reported to be of value. 109 patients with a mean age of 55 years and a median follow-up of 25 months were examined. Vessels were immunohistochemically highlighted using an antibody to platelet endothelial cell adhesion molecule CD31, and microvessel density was quantified using a Chalkley point eyepiece graticule. No significant correlation was observed with patient age, tumor size, grade, ER, or EGFR expression. In a univariate analysis of survival, whereas ER expression was not a significant indicator of either relapse-free (RFS) or overall survival (OS), vascular count (VC) predicted both early RFS and OS (p = 0.01) and p = 0.028 respectively). Furthermore, in patients with ER positive tumors, a subgroup usually considered to have a good prognosis, there was a significant reduction in RFS and OS if tumors had high VCs (p = 0.05 and p = 0.002 respectively). A further statistically significant reduction in RFS (p = 0.05) was observed for EGFR positive highly vascular tumors.(ABSTRACT TRUNCATED AT 250 WORDS)