['To describe the incidence of low-volume ultrastage-detected metastases in sentinel lymph nodes (SLNs) identified at surgical staging for endometrial carcinoma and to correlate it with depth of myoinvasion and tumor grade.', 'We reviewed all patients who underwent primary surgery for endometrial carcinoma with successful mapping of at least one SLN at our institution from September 2005 to December 2011. All patients underwent a cervical injection for mapping. The SLN ultrastaging protocol involved cutting an additional 2 adjacent 5-μm sections at each of 2 levels, 50-μm apart, from each paraffin block lacking metastatic carcinoma on routine hematoxylin and eosin (H&E) staining. At each level, one slide was stained with H&E and with immunohistochemistry (IHC) using anticytokeratin AE1:AE3.Micrometastases (tumor deposits >0.2 mm and ≤2 mm) and isolated tumor cells (≤0.2 mm) were classified as low-volume ultrastage-detected metastases if pathologic ultrastaging was the only method allowing detection of such nodal disease.', 'Of 508 patients with successful mapping, 413 patients (81.3%) had endometrioid carcinoma. Sixty-four (12.6%) of the 508 patients had positive nodes: routine H&E detected 35 patients (6.9%), ultrastaging detected an additional 23 patients (4.5%) who would have otherwise been missed (4 micrometastases and 19 isolated tumor cells), and 6 patients (1.2%) had metastatic disease in their non-SLNs. The incidence rates of low-volume ultrastage-detected nodal metastases in patients with grades 1, 2, and 3 tumors were 3.8%, 3.4%, and 6.9%, respectively. The frequency rates of low-volume ultrastage-detected metastases in patients with a depth of myoinvasion of 0, less than 50%, and 50% or more were 0.8%, 8.0%, and 7.4%, respectively. Lymphovascular invasion was present in 20 (87%) of the cases containing low-volume ultrastage-detected metastases in the lymph nodes.'] Does pathologic ultrastaging improve micrometastasis detection in sentinel lymph nodes during endometrial cancer staging?