Herein, we are presenting a case of a 33-year-old woman who presented to the emergency department complaining of persistent lower abdominal pain of one-day duration. Physical examination revealed abdominal tenderness with right lower quadrant rebound tenderness. Computed tomography abdomen/pelvis showed a 6 cm possible necrotic mass of the left ovary with moderate amount of complex ascites. A laparoscopic left oophorectomy with bilateral salpingectomy, right ovarian biopsy, and appendectomy were performed without complications. The cut surface of the left ovary showed a 9.7 cm × 8 cm × 4 cm ovarian mass, and the cut surface revealed multiple gray-tan friable papillary excrescence. Microscopic evaluation showed findings consistent with left and right ovarian serous borderline tumor (SBT). Subsequently, a tumor staging was conducted with total laparoscopic hysterectomy, pelvic and periaortic lymph node dissection, and omentectomy. The endometrium sections showed several small foci of SBT within the endometrial stroma, consistent with non-invasive implants of the endometrium. The omentum and lymph nodes were all negative for malignancy. SBTs associated with endometrial implants are very rare with only one case reported in the literature. Their existence can cause diagnostic challenges, and they should be acknowledged for early diagnosis and to plan for patient’s treatment and outcome.