The association of ovarian malignancy with pregnancy is rare; accounting for 3–6% of ovarian masses of which malignant germ cell tumors represent the type most frequently associated with pregnancy, whereas the incidence of epithelial ovarian cancer is only 1/12,000 to 1/50,000 of pregnancies. The diagnosis and management of ovarian cancer in pregnancy remain poorly codified because of the rarity of cases and the limited data available on this pathology. We report here the case of a 33-year-old woman with a low-grade invasive serous carcinoma of the left ovary diagnosed during pregnancy, identified by ultrasound and magnetic resonance imaging. The patient was treated by surgical resection followed by adjuvant chemotherapy without interrupting the pregnancy because she refused to. A c-section was programmed at 36 weeks of gestation with complement of surgery.