Sentinel lymph node (SLN) biopsy is a new standard of care for axillary node staging in breast cancer, which for the first time allows enhanced pathologic analysis on a routine basis. Although a number of retrospective studies, including our own series with 20-year follow-up, suggest that axillary nodal micrometastases found in this manner are prognostically significant, prospective trials now under way promise a definitive answer to this controversial subject. Enhanced pathology using serial sections and immunohistochemical staining identifies a high-risk minority of conventionally node-negative patients who are converted to node-positive and thereby become candidates for systemic adjuvant chemotherapy. The developmental phase of SLN biopsy, now drawing to a close, has focused on the identification of this node-positive group. Enhanced pathology also identifies a majority of patients who are truly node-negative and whose expectation of long-term survival exceeds that of historic norms for node-negative breast cancer. The next era of SLN biopsy should focus on the characterization of this group. SLN biopsy in breast cancer has already extended the historic trend toward surgical conservatism. By defining more precisely a low-risk cohort of patients, SLN biopsy has the potential to initiate a trend toward medical conservatism as well.