In order to define the term "a node-negative patient", the axillary nodal status at the primary operation for breast cancer was evaluated in 13,851 patients registered by the Danish Breast Cancer Cooperative Group (DBCG). The determinants for node negativity in primary breast cancer were the number of lymph nodes removed and the tumour size. The number of lymph nodes removed should be at least 10 to exclude misclassification of node-positive patients as node negative. There was a strong relationship between tumour size and the percentage of node-negative patients. Another observation was that high rate of node negativity was associated with low histological grade. The age of the patients had no influence on node negativity. Where 10 or more negative lymph nodes were removed, significantly better axillary recurrence-free survival (P less than 0.0001), over-all recurrence-free survival (P less than 0.0001) and survival (P less than 0.005) were found.