OBJECTIVE The authors report the feasibility and accuracy of intraoperative lymphatic mapping with sentinel lymphadenectomy in patients with breast cancer. BACKGROUND Axillary lymph node dissection (ALND) for breast cancer generally is accepted for its staging and prognostic value, but the extent of dissection remains controversial. Blind lymph node sampling or level I dissection may miss some nodal metastases, but ALND may result in lymphedema. In melanoma, intraoperative lymph node mapping with sentinel lymphadenectomy is an effective and minimally invasive alternative to ALND for identifying nodes containing metastases. METHODS One hundred seventy-four mapping procedures were performed using a vital dye injected at the primary breast cancer site. Axillary lymphatics were identified and followed to the first ("sentinel") node, which was selectively excised before ALND. RESULTS Sentinel nodes were identified in 114 of 174 (65.5%) procedures and accurately predicted axillary nodal status in 109 of 114 (95.6%) cases. There was a definite learning curve, and all false-negative sentinel nodes occurred in the first part of the study; sentinel nodes identified in the last 87 procedures were 100% predictive. In 16 of 42 (38.0%) clinically negative/pathologically positive axillae, the sentinel node was the only tumor-involved lymph node identified. The anatomic location of the sentinel node was examined in the 54 most recent procedures; ten cases had only level II nodal metastases that could have been missed by sampling or low (level I) axillary dissection. CONCLUSIONS This experience indicates that intraoperative lymphatic mapping can accurately identify the sentinel node--i.e., the axillary lymph node most likely to contain breast cancer metastases--in some patients. The technique could enhance staging accuracy and, with further refinements and experience, might alter the role of ALND.