We present a case of incidental locally advanced serous papillary ovarian carcinoma in a 43-year-old women on endometrial biopsy. On endometrial biopsy, findings of serous carcinoma besides normal endometrial tissue caused diagnostic confusion. However, by thorough clinical investigation, we were able to detect bilateral ovarian masses, which were proved to be serous papillary cystadenocarcinoma. The possibility of a locally advanced ovarian carcinoma should always be kept in mind especially when trying to identify a serous papillary carcinoma in an endometrial biopsy with no endometrial involvement.