Pelvic ultrasonography and measurement of serum cancer antigen 125 (CA-125) are recommended for preoperative evaluation before performing risk-reducing salpingo-oophorectomy (RRSO). We report our experience with two patients in whom an incidental gynaecological malignancy was found using endometrial cytology as a preoperative screening test for RRSO. Patient 1 was an early 50s woman with a pathologic variant of BRCA1 Transvaginal ultrasonography showed no endometrial abnormalities, but preoperative endometrial cytology revealed high-grade serous carcinoma. The patient underwent total hysterectomy, bilateral adnexectomy, pelvic and para-aortic lymph node dissection, and omentectomy. Patient 2 was a late 40s woman with a pathological variant of BRCA1 Transvaginal ultrasonography showed mild enlargement of the left ovary, and her CA-125 level was elevated. Preoperative endometrial cytology revealed high-grade serous cancer. She underwent total hysterectomy, bilateral adnexectomy and omentectomy. These case reports illustrate the importance of preoperative screening-including endometrial cytology-before performing RRSO.