The goal of this study was to evaluate the periareolar injection of technetium 99m sulfur colloid to identify axillary sentinel nodes and compare the number of sentinel lymph nodes identified with preoperative lymphoscintigraphy to intraoperative biopsy using a handheld gamma probe. A total of 104 consecutive patients diagnosed with invasive breast cancer participated in this prospective study, with 81 patients receiving an intradermal periareolar injection and 23 patients receiving an intradermal peritumoral injection of filtered technetium 99m sulfur colloid. Preoperative lymphoscintigraphy was performed for sentinel node mapping and localization. In addition to selective sentinel node biopsy, axillary dissection was performed on all patients to determine false-negative rates. Routine histologic staining was performed on all identified nodes, along with immunohistochemical staining of sentinel nodes negative on initial routine staining. With an intradermal periareolar injection, the sentinel node identification rate was 91.4% (74/81), axillary metastatic rate 35.1% (26/74), sentinel node positive only 61.5% (16/26), and false negative 3.8% (1/26). With an intradermal peritumoral injection, the sentinel node identification rate was 91.3% (21/23), axillary metastatic rate 42.9% (9/21), sentinel node positive only 88.9% (8/9), and false negative 0% (0/9). A total of 241 sentinel nodes were identified with biplanar lymphoscintigraphy and 173 sentinel nodes were harvested during surgery, yielding a 28.2% increase in sentinel nodes identified with lymphoscintigraphy. This study demonstrates that intradermal periareolar injection of filtered technetium 99m sulfur colloid is successful in identifying axillary sentinel nodes with a low false-negative rate. Preoperative lymphoscintigraphy aids in the identification and surgical planning of sentinel node biopsy and provides an objective measure of surgical performance.