The purpose of this study was to examine predictors of lymph node (LN) metastases or extrauterine disease (ED) in low-grade (FIGO grade 1 or 2) endometrioid carcinoma (LGEC) in a multi-institutional setting. For LGEC with and without LN metastasis or ED, each of the 9 participating institutions evaluated patients' age, tumor size, myometrial invasion (MI), FIGO grade, % solid component, the presence or absence of papillary architecture, microcystic, elongated, and fragmented glands (MELF), single-cell/cell-cluster invasion (SCI), lymphovascular invasion (LVI), lower uterine segment (LUS) and cervical stromal (CX) involvement, and numbers of pelvic and para-aortic LNs sampled. A total of 304 cases were reviewed: LN(+) or ED(+), 96; LN(-)/ED(-), 208. Patients' ages ranged from 23 to 91 years (median 61 y). Table 1 summarizes the histopathologic variables that were noted for the LN(+) or ED(+) group: tumor size ≥2 cm, 93/96 (97%); MI>50%, 54/96 (56%); MELF, 67/96 (70%); SCI, 33/96 (34%); LVI, 79/96 (82%); >20% solid, 65/96 (68%); papillary architecture present, 68/96 (72%); LUS involved, 64/96 (67%); and CX involved, 41/96 (43%). For the LN(-)/ED(-) group, the results were as follows: tumor size ≥2 cm, 152/208 (73%); MI>50%, 56/208 (27%); MELF, 79/208 (38%); SCI, 19/208 (9%); LVI, 56/208 (27%); >20% solid, 160/208 (77%); papillary architecture present, 122/208 (59%); LUS involved, 77/208 (37%); CX involved, 24/208 (12%). There was no evidence of a difference in the number of pelvic or para-aortic LNs sampled between groups (P=0.9 and 0.1, respectively). After multivariate analysis, the depth of MI, CX involvement, LVI, and SCI emerged as significant predictors of advanced-stage disease. Although univariate analysis pointed to LUS involvement, MELF pattern of invasion, and papillary architecture as possible predictors of advanced-stage disease, these were not shown to be significant by multivariate analysis. This study validates MI, CX involvement, and LVI as significant predictors of LN(+) or ED(+). The association of SCI pattern with advanced-stage LGEC is a novel finding.