Objective: To compare pre-surgical demographic and clinical factors and preoperative serum tumor marker values of patients with endometrial and ovarian synchronous carcinoma with those diagnosed with endometrial carcinoma with metastatic ovarian involvement (FIGO stage IIIA). Methods: A retrospective observational study including patients with endometrial and ovarian malignant tumors that were treated at Miguel Servet University Hospital, Zaragoza, Spain, since January 2000 to June 2020. All pathologic specimens were reviewed by two pathologists specialized in gynecological oncology. Results: Overall, 51 patients were included. 24 cases of them, were endometrial and ovarian synchronous primary carcinomas and the remaining 27 cases were endometrial tumors with adnexa. Parity, personal and family oncological history, arterial hypertension, diabetes, dyslipidemia, obesity and the prior use of hormone replacement therapy did not show significant differences between both groups. Age (p = 0.002), menopausal status (p = 0.029), abnormal uterine bleeding (p = 0.001), Ca 12.5 preoperative serum level (p = 0.038) and Ca 19.9 preoperative serum level (0.028) were factors with significant differences between both groups. In multivariate analysis, only abnormal uterine bleeding and Ca 19.9 values were independents factors. Conclusions: The presence of abnormal uterine bleeding and Ca 19.9 preoperative serum level could guide the clinician in the preoperative differential diagnosis between endometrial cancer with ovarian involvement and endometrial and ovarian synchronous carcinoma.