Metastases to the axillary nodes, the internal mammary nodes, or both, define a group of patients at very high risk of having systemic micrometastases leading to recurrent disease and death if surgical therapy alone is used. In our review of 7,070 patients with breast cancer in whom both axillary nodes and internal mammary nodes were examined histologically, 5% to 10% had internal mammary node metastases in the absence of axillary node metastases. With the availability of effective systemic therapy that can improve the survival of patients with operable breast cancer who have lymph node metastases, information obtained from internal mammary node biopsies assumes practical significance. Our current policy is to perform internal mammary node biopsies on patients with operable breast cancer who have medial and central primary tumors of any size and lateral primary tumors 2 cm or greater in diameter if a frozen section of the most suspicious node in the axillary dissection shows no histologic evidence of metastasis.