Serous endometrial intraepithelial carcinoma (SEIC) is a rare but highly aggressive form of uterine endometrial cancer. We report two cases of post-menopausal, 58-year-old patients with abundant vaginal bleeding and pelvic pain. The first patient had a history of surgical hysteroscopy in 2019 for an endocervical polyp. The second patient had a history of breast resection, axillary lymph node dissection, chemotherapy, radiation therapy, and tamoxifen therapy for breast carcinoma 6 years ago. An abdominal hysterectomy was performed in both patients. The pathological assessment showed serous endometrial intraepithelial carcinoma. Diagnosis of a serous proliferation of the uterus implies the exploration of other genital tract organs as well as distant locations in search of metastatic disease.