In 164 breast carcinomas the presence of peritumoral lymphatic vessel invasion (PLVI) was evaluated and correlated with other known indicators of prognosis and with the clinical outcome of the patients. Overall 22% of tumors were PLVI-positive. The presence of PLVI was significantly associated with axillary node involvement (p less than 0.0001) and tumor size (p = 0.005), and tended toward an association with grading (p = 0.065). No significant association was found between PLVI and steroid hormone receptors, DNA ploidy, or proliferative activity. Univariate analysis shows that peritumoral vessel invasion was significantly associated with a higher risk of recurrence (p = 0.012) and with a trend toward shorter survival (p = 0.074). Besides the presence of PLVI, prognosis was significantly worse also for patients with high proliferative aneuploid tumors and with axillary node metastases. Moreover, within the subsets of patients generally considered to have good prognosis, the presence of PLVI identified patients with a trend for higher risk such as those with PLVI-positive diploid tumors, PLVI-positive low-proliferative tumors, and PLVI-positive node-negative tumors. Adopting multivariate analysis, PLVI failed to retain prognostic importance when adjusted for node status, DNA ploidy, and proliferative activity. In conclusion, we found that the presence of PLVI has prognostic significance when singly evaluated. Multivariate analysis shows that PLVI is not an independent prognostic factor in stage I-II breast cancer.