Borderline ovarian tumors (BOTs) have low malignant potential and favorable prognoses. The group of patients most affected by BOTs are women of childbearing age; therefore, fertility-sparing surgery is considered the first choice of treatment for young patients. Several studies have reported that conservation treatment was associated with a higher recurrence rate; however, data on the treatment and clinical management of patients after relapse are scarce. A 19-year-old woman was admitted to our hospital for two weeks due to unexplained abdominal distension. Palpation of the uterus showed no significant abnormality, but an ultrasound examination revealed abdominal effusion and a solid cystic mass in front of the uterus. Since the patient wanted to preserve fertility, she underwent fertility-sparing procedures, including abdominal right adnexectomy and excision of the left ovarian mass. Histological examination confirmed stage III serous BOTs (desmoplastic non-invasive implants associated with ovarian serous borderline tumor). After the surgery, the patient had normal menstruation. After 20 months, the patient experienced a recurrence of serous type BOTs (stage IIIC; serous carcinoma, non-invasive, low grade, ICD-O: 8460/2), and a second fertility-sparing surgery was performed. Presently, although no disease recurrence was detected at the last follow-up, the patient had no menses for six months and had not yet completed childbirth. In young women diagnosed with BOTs, fertility preservation surgery might be associated with a high risk of recurrence, especially for those with advanced staged disease. Clinically, pregnancy should be recommended as early as possible after surgery, and long-term follow-up is required.