The purpose of this study was to examine predictors of lymph node metastases (LN+) or extrauterine disease (ED) in low grade (FIGO grades 1 or 2) endometrioid carcinoma (LGEC) in a multi institutional setting. For LGEC with and without LNM 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) and single cell/cell cluster invasion (SCI), lymphovascular invasion (LVI), lower uterine segment (LUS) and cervical stromal (CX) involvement and numbers of pelvic (PLN) and para-aortic (PALN) LNs sampled.302 cases were reviewed: LN+ or ED +, 96; LN-/ED-, 208. Patients' ages ranged from 23-91 yrs (median 61). Table 1 summarizes the histopathologic variables that were noted for the LN+ or ED+ group: tumor size ≥2cm, 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, 31/96 (32%). For the LN-/ED- group, the results were as follows: tumor size ≥2cm, 152/208 (73%), MI >50%, 56/208 (27%), MELF, 79/208 (38%), single cell invasion, 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, 31/208 (15%). 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). Following multivariate analysis, depth of myometrial invasion, cervical stromal involvement, lymphovascular space invasion, and the single cell pattern of invasion 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 LV as significant predictors of LN+ or ED. The association of SCI pattern with advanced stage LGEC is a novel finding.