No standard method for handling and histopathologic examination of the sentinel node (SN) exists. We hypothesized that a focused examination of all nodes with serial sectioning and cytokeratin immunohistochemical staining would confirm the SN as the node most likely to harbor metastasis. Intraoperative lymphatic mapping and sentinel lymphadenectomy using blue dye and (99m)technetium-labeled sulfur colloid were performed. All nodes were stained with H&E. All tumor-free nodes underwent additional sectioning and staining with H&E and an immunohistochemical stain. Routine H&E examination detected SN metastases in 27.6% of cases. Occult SN metastases were identified in 12.7% of cases. None of the 724 non-SNs examined contained occult metastases. The SN false-negative rate was zero. This study confirms histopathologically that the SN has biologic significance as the axillary node most likely to harbor metastatic tumor Standardization of the handling, sectioning, and staining of the SN is necessary as lymphatic mapping and sentinel lymphadenectomy become integrated into the care of patients with breast cancer