Aim: The clinicopathologic characteristics, recurrence patterns, and survival of patients with grade 3 endometrial cancer (G3-EAC) and uterine carcinosarcoma (UCS) were compared. Materials and Methods: The medical records of patients treated for G3-EAC and UCS between January 1996 and December 2016 at 11 gynecologic oncology centers in Turkey and Germany were analyzed. Results: Of all patients included in the study, 161 (45.1%) were diagnosed with UCS and 196 (54.9%) with G3-EAC at FIGO stage I-II (early stage) disease. The recurrence rate was higher in patients with UCS than in those with G3-EAC (17.4 vs. 9.2%, p = 0.02). The 5-year disease-free survival (DFS; 75.2 and 80.8%, respectively; p = 0.03) and overall survival (OS; 79.4 and 83.4%, respectively; p = 0.04) rates were significantly lower in the UCS group compared to the G3-EAC group. UCS histology was an independent prognostic factor for decreased 5-year DFS (HR 1.8, 95% CI 1.2-3.2; p = 0.034) and OS (HR 2.7, 95% CI 1.3-6.9; p = 0.041) rates. Conclusions: The recurrence rate was higher in UCS patients than in G3-EAC patients, regardless of disease stage. DFS and OS were of shorter duration in UCS than in G3-EAC patients. Adequate systematic lymphadenectomy and omentectomy were an independent prognostic factor for increased 5-year DFS and OS rates.