For endometrial cancer (EC), most surgeons rely on intraoperative frozen section (IFS) to determine the risk of nodal metastasis and necessity of lymphadenectomy. IFS remains a weak link in this practice due to its susceptibility to diagnostic errors. As a less invasive alternative, sentinel lymph node (SLN) mapping and ultra-staging have gradually gained acceptance for EC. We aimed to establish the SLN success rate, negative predictive value, and whether SLNs provide useful information for cases misdiagnosed on IFS. From 2013 to 2017, 100 patients (63 low-risk and 37 high-risk EC) underwent hysterectomy, bilateral salpingo-oophorectomy, and SLN. Among them, 56 had additional pelvic lymphadenectomy. A total of 337 SLNs were obtained in 86 cases: 55 bilaterally and 31 unilaterally. The remaining 14 cases failed because of patient obesity or leiomyoma. Pathology ultra-staging detected 2 positive SLNs from 2 patients (1 with isolated tumor cells, 1 with micrometastases). One of 773 nonsentinel pelvic nodes was positive on the contralateral hemi-pelvis in a patient who was mapped unilaterally, resulting in negative predictive value of 100%. During IFS, tumor grade and/or depth of myometrial invasion was misdiagnosed in 22 cases (22%). These errors would have resulted in under-staging in 10 high-risk patients or over-staging in 4 low-risk patients. SLNs were mapped in these misestimated patients, with one revealing metastases. SLN provides invaluable information on nodal status while detecting occult metastases in cases misdiagnosed on IFS. Our findings justify the incorporation of SLN in initial surgery for EC as an offset to IFS diagnostic errors, minimizing their negative impact on patient care.