Multimodal treatment, including assisted reproductive technology, is necessary in young patients with advanced borderline ovarian tumors. However, the details of long‐term follow‐up cases have not been reported. In this report, a 19‐year‐old patient presented with a stage IIIC serous borderline tumor. The patient underwent five fertility‐sparing surgeries. The tumor did not respond to any of the three lines of chemotherapy administered. Serological and radiological responses were observed following hormonal treatment with leuprorelin, followed by a fourth surgery. Before the planned fifth surgery for complete resection of both adnexa, cryopreservation of the fertilized eggs was performed. At age 36, when the disease‐free interval exceeded the previous one, we proposed embryo transfer; however, she declined fertility treatment. The patient had developed rheumatoid arthritis and childbirth not a priority. The patient had lived without any evidence of disease for 7 years following the last surgery and 20 years after the initial visit. [ABSTRACT FROM AUTHOR]