Blood vessel invasion and axillary lymph node involvement were examined in 175 breast cancer patients. The incidence of blood vessel invasion was 35%. The presence of blood vessel invasion was highly associated with early disease recurrence. The association of poor prognosis with blood vessel invasion was independent of clinical stage, menopausal status, node status, tumor size, or postsurgical treatment. Those patients with blood vessel invasion and two or more positive nodes were at extremely high risk for early recurrence (70% recurrence by two years compared with 15% recurrence in the remainder of the patients). Thus, blood vessel invasion is a useful indicator of early recurrence in patients with primary breast cancer and, in combination with node status, is a prognostic indicator with high discriminatory power.