The presence of tumour cells in the efferent vessels of the axillary nodes of breast cancer patients is termed efferent vascular invasion (EVI). The EVI status had been recorded in 112 cases which have now been followed for a mean of 120 ± 8 months. At the start of the 10th year 17 per cent. of the EVI positives cases were alive, compared to 54 per cent. of the EVI negative. The EVI status has thus strong prognostic implications. It can be recorded in association with primary treatment on routine histological examination. No special equipment is required.