Historically known as a "silent killer", ovarian cancer is often diagnosed at an advanced stage. We describe an unusual case of stage I, ovarian, high-grade serous carcinoma detected by a routine Papanicolaou (PAP) smear, with no abnormal physical, imaging, or laboratory findings. A 53-year-old woman with newly diagnosed triple-negative breast cancer received a screening Pap smear, which showed malignant cells not coming from the breast or uterine cervix. Pelvic examination, cervical biopsy, and gynecologic ultrasonography found no abnormality. Endometrial curettage yielded free-floating adenocarcinoma cells. The immunohistochemical stain result indicated ovary or fallopian tube cancer. Complete cytoreductive surgery was performed, and high-grade serous carcinoma of bilateral ovaries, FIGO stage IB, was diagnosed. Although extremely rare, when malignant cells not originating from the uterine cervix are detected on a Pap smear, it may lead to an early diagnosis of ovarian cancers, and this warrants further comprehensive workup.