Vascular invasion was identified as an important prognostic variable for all lesion sizes in 138 patients with Stage I cervical carcinoma. A matched pairs analysis, controlling for lesion size and extracervical spread, showed that vascular invasion was significantly associated with poor outcome. Regression analysis also indicated that vascular invasion contributed prognostic information beyond that available from lesion size and extracervical spread. Studies of adjunctive therapy based on the prognostic variables are recommended.