Most borderline ovarian tumors (BOT) occur in young women and exhibit a low malignant behavior. Nevertheless, an accurate long-term follow-up is required because, frequently, recurrence arises after many years from primary treatment, especially in patients affected by BOT with invasive peritoneal implants, which have a worse prognosis. We report the case of a pelvic recurrence of serous BOT firstly suspected by physical examination but misdiagnosed by ¹⁸F-fluorodeoxyglucose positron emission tomography and computed tomography and identified only by magnetic resonance imaging, 7 years after primary treatment. We also reviewed the literature concerning the role of ¹⁸F-fluorodeoxyglucose positron emission tomography in the management and follow-up of BOT.