The aim of this study is to assess the type and degree of correlation of prognostic factors with the degree of myometrial invasion (MI) in subjects with endometrial cancer (EC). The research included 60 female subjects hospitalized for a planned surgical procedure, due to histopathologically (PHD) proven EC in the period from 2019 to 2021. The following parameters were monitored and analyzed: histopathological parameters: histological type, MI in millimeters and percentages, distance of the tumor from the serosa, lymphovascular invasion, invasion of the stroma and mucosa of the cervix, invasion of the ovary or uterine tube, lymph node metastases, and the International Federation of Gynecology and Obstetrics (FIGO) stage. Patients were divided into two groups, after surgery and PHD assessment of MI degree, into those with less than and more than 50% MI. Statistical data processing was done in the SPSS 24.0 software package (Chicago, IL, USA). Out of the total number of patients (60), MI <50% was present in 34 (56.6%) patients, and >50% in 26 (43.4%). Our study showed that the anteroposterior (AP) diameter of the EC and the uterine wall is significantly larger with >50% myometrial invasion, while the AP diameter of the remaining myometrium is significantly smaller. A significant finding of our study is that the cut-off value of 11 mm for the distance of EC from the serosa correlates with the degree of MI. Based on the results of our study, we came to the conclusions that the degree of MI >50% correlates with the AP diameter of the EC, the distance of the tumor from the serosa, and that it is a significant predictor of the existence of lymphovascular invasion, invasion of the uterine cervix and adnexa.