Introduction: This study aimed to compare histological grades in patients with endometrial cancer assessed by pre- and postoperative techniques. Methods: We retrospectively reviewed the records of 43 patients operated on for endometrial cancer between 2012 and 2019. The primary dependent variables included histological grade assessed by preoperative probe curettage and postoperative analysis of surgical specimens. The independent variables included age, surgery type (laparoscopy or laparotomy), pre- and postoperative hemoglobin levels, and the length of hospital stay. Results: The mean age was 62.14 ± 9.14 years, and the length of hospitalization time was 6.51 ± 3.46 days. The mean values of pre- and postoperative hemoglobin levels were 12.44 ± 1.51 mg/dL and 10.91 ± 1.28 mg/dL, respectively. According to the grading results of probe curettage, grade 1, 2, and 3 tumors were found in 21 (48.8%), 19 (44.2%), and 3 (7.0%) patients, whereas the paraffin sections revealed grade 1, 2, and 3 in 12 (27.9%), 22 (51.2%), and 9 (20.9%) patients, respectively. There was a fair but statistically significant agreement between the pre- and postoperative grading (kappa = 0.365, p = 0.001). Discussion: This study confirms literature reports that preoperative histological tumor grade fairly predicts final histological results. Caution is warranted when making clinical decisions solely based on probe curettage. Further improvements in preoperative diagnostic techniques in endometrial cancer are needed.