ObjectiveTo identify the predictors of coexisting adnexa malignancy (CAM) before surgery for patients with G1/G2 endometrioid endometrial cancer (EEC). MethodsPatients with G1/G2 EEC who received surgery in Fudan University Shanghai Cancer Center from 1996 to 2017 were enrolled. Univariate and multivariate logistic regression were performed to identify the predictors for CAM, and the nomogram was constructed and evaluated the discrimination and calibration. ResultsAmong the 1511 patients in the study cohort, 66 (4.4%) coexisted adnexa malignancy (51 metastatic and 15 synchronous primaries). In the univariate logistic regression analysis, CA125 level (>35 U/ml), histologic grades, myometrial invasion depth in magnetic resonance imaging (MRI), adnexal involvement in MRI/surgical exploration (SEP) were found to be significant predictors for CAM (P < .001, 0.047, 0.011, <0.001, respectively). The multivariate analysis demonstrated that high CA125 level (P < .001; OR: 2.945; 95%CI: 1.700–5.101), deep myometrial invasion (P = .011; OR: 2.194; 95%CI: 1.200–4.011), and suspected adnexal involvement in MRI/SEP (P < .001; OR: 11.524; 95%CI: 6.726–19.744) were independent predictors for CAM (AUC = 0.786). In 338 patients with MMR results, eighty-seven (25.7%) were detected MSI-high. There were 5.7% (5/87) patients diagnosed with CAM in the MSI-high group compared with 4.4% (11/251) in the MSS group. ConclusionsA nomogram with pre- and intra-operative factors was constructed to predict CAM in G1/G2 EEC patients, which may help clinicians in decision-making for ovarian preservation for these patients.