Objective: This study aims to determine the frequency of ovarian involvement in patients aged 50 years and younger, investigate the associated factors, and, unlike other studies in the literature, investigate the role of the systemic immune-inflammatory index (SII) in ovarian involvement. Material and Methods: Patients aged 50 years and younger with endometrial cancer between 1992 and 2022 were included in the study. Patients were examined in two groups: patients with adnexal involvement (ovarian metastasis and synchronous ovarian cancer) and patients without adnexal involvement. Clinicopathological parameters that can be used to predict adnexal involvement were analyzed in both groups. Complete blood count parameters (platelet, leukocyte, lymphocyte, neutrophil) were analyzed from the preoperative patients. To evaluate inflammatory indices, PLR (platelet/lymphocyte), NLR (neutrophil/lymphocyte) and SII (neutrophil x platelet/lymphocyte) were calculated. A two-group analysis was performed between the groups by determining the cut-off value for the statistically significant parameters. Results: A total of 205 patients were included in the study, and histopathological ovarian metastasis was detected in 5.9% (n=12), synchronous ovarian tumor was detected in 2.4% (n=5). In the univariate analysis, non-endometrioid histological type, increased grade, advanced stage disease, myometrial invasion depth, LVSI, cervical stromal invasion, lymph node metastasis and omental involvement indicate an increased risk for ovarian involvement (p>0.005). However, in the regression analysis (Table 2) only the stage of the disease, cervical stromal invasion, metastatic pelvic lymph node and omental involvement were found to be independent risk factors for ovarian involvement (p<0.001). Preoperative laboratory values of the patients were examined and a statistically significant difference was found in neutrophil count, NLR percentage and SII (p<0.005). In the group with ovarian involvement, median SII was 1201.62 (±631.95), higher than the group without ovarian involvement (p= 0.023). In the ROC analysis, the best cut-off points were 70% sensitivity, 76% specificity and 992.58 cut-off value (AUC=.726) for SII.When the patients were grouped according to the cut-off value of 992, ovarian involvement was significantly more common in the presence of high SII (p<0.005). Conclusion: Due to the adverse effects of early menopause on women’s health, an ovarian preservation approach for endometrial cancer was brought to the agenda. This study shows that ovarian involvement is rare in patients younger than 45 years of age, with low grade, superficial myometrial invasion, no cervical stromal involvement, no LVSI, and no intraoperative extrauterine spread. In these patients, ovarian-sparing surgery should be considered an option, and SII can be used as an index to be considered in patient selection.