Survival in breast cancer correlates with the presence of metastatic lymph nodes, so that removal and pathological examination of the axillary nodes provides the most important prognostic information and basis for planning subsequent therapy. However as the size of primary tumours at diagnosis is decreasing, the likelihood of axillary involvement is also declining, so that the indications for axillary dissection are undergoing radical revision. To definitively establish the value of removing all three axillary lymph node levels (as defined by Berg) in node positive breast cancer, retrospective analysis of a large series receiving complete dissection was carried out. consecutive breast cancer patients (n=1003) with positive axillary nodes were analyzed: all received identical axillary treatment and the three levels were tagged with metal disks to facilitate recognition and pathological examination. Follow-up (mean 97 months) was exceptionally complete. The length of disease-free and overall survival were taken as the primary endpoints. The variables considered in the statistical analysis were tumour size, number of metastatic nodes, axillary invasion by level (the three classic levels), perilymphnodal invasion and age. By univariate analysis, overall and disease-free survival decreased significantly as tumour diameter, number of involved lymph nodes, and involvement by axillary level increased. Multivariate analysis assessing the relative importance of these variables when all were considered together found that they were all important independent predictive factors for survival. This study confirms the importance of tumour size and number of metastatic axillary nodes as predictors of outcome in breast cancer. In addition, the level of axillary invasion as a third independent factor of equal importance to the established indicators was identified. When axillary dissection is performed it should be complete, and all three Berg levels tagged separately, so that involvement by level can be ascertained. This provides additional important prognostic information on which to base subsequent treatment decisions.