There is a risk of overlooking lymph node metastases and thereby contributing to inaccurate nodal staging when performing partial axillary dissection in conjunction with total mastectomy in female breast cancer. The Danish Breast Cancer Cooperative Group (DBCG) analysed this risk in a prospective nation-wide adjuvant trial dealing with primary operable breast carcinoma. The series comprised 3114 patients, initially found to have lymph node negative axillae, followed for a median of 24 months (quartiles 12-40). It was found that the probability of early ipsilateral axillary relapse of cancer, estimated by means of the life table method, decreased with the number of nodes removed. After 2 years the recurrence rate was 12 per cent for patients with no lymph nodes removed, 7 per cent with one or two nodes removed and 2 per cent with three or more nodes removed. It is concluded that the risk of false negative nodal staging in conjunction with partial axillary dissection is modest, provided at least three lymph nodes are removed and found to be negative on histological examination.