Lymphoscintigraphy (LS) may identify sentinel lymph nodes (SLNs) outside the axilla. Biopsy of these nodes could improve the accuracy of lymphatic mapping (LM) for breast cancer (BC) if a significant number of tumor-positive extra-axillary sentinel nodes are identified. To address this, we evaluated the impact of the use of preoperative LS and biopsy of axillary and internal mammary SLNs in women with BC. From October 1997 to July 2003, 175 women with breast cancer received technetium sulfur colloid, and images were obtained. Isosulfan blue dye was injected intraoperatively, and LM of the axillary and internal mammary lymph node basins was performed with a hand-held gamma probe. The anatomic location and histologic status of all SLNs identified with LS and LM was recorded, and the impact of the findings on LS and internal mammary LM were evaluated. LS showed SLN in 127/175 (73%) women and "hot spots" were found with the gamma probe in 142/175 (81%). At least one SLN was identified by LM in 168/175 (96%) patients, and 48/168 (29%) had metastases. One hundred sixty-two of 168 (96%) patients had SLN exclusively in the axilla. Only 10 of 175 (6%) women had internal mammary (IM) SLNs seen on LS. LM identified IM sentinel nodes in 6 of these 10 patients, but none were involved with tumor. Preoperative lymphoscintigraphy and biopsy of internal mammary sentinel nodes do not enhance the accuracy of lymphatic mapping for breast cancer. Omitting lymphoscintigraphy reduces the complexity and cost of lymphatic mapping without compromising the identification of tumor-positive sentinel nodes.