Serous tubal intraepithelial carcinoma (STIC) is considered the precursor of pelvic serous carcinomas and the earliest malignant alteration in BRCA mutation-positive women. Recently, risk-reducing salpingo-oophorectomy (RRSO) is being performed in BRCA mutation- positive women and STIC is often discovered incidentally in the fallopian tubes. A 62-year-old woman underwent bilateral salpingo-oophorectomy (BSO) for ovarian cysts. Ten months later, cytological screening for the endometrium revealed adenocarcinoma. No atypical tissue was detected by the endometrial curettage. Imaging tests and hysteroscopy found no abnormal findings. She underwent hysterectomy and was diagnosed with STIC originating from the intrauterine portion of the residual fallopian tube. Here, the authors report the first case of STIC being detected during an endometrial cytological examination after BSO. Although STIC associated with the BRCA mutation usually involves the distal fallopian tube, the present case suggests that the intrauterine portion of the fallopian tube should be removed or cauterized during RRSO.