Objective: To report on ovarian carcinoma development after cystectomy for a borderline mucinous ovarian tumor. Design: Case report. Setting: A French comprehensive cancer center. Patient(s): One patient who developed recurrence in the form of an invasive ovarian carcinoma after simple cystectomy for a borderline mucinous ovarian tumor. Intervention(s): Simple cystectomy. Main Outcome Measure(s): Clinical outcome. Result(s): A 22-year-old nulliparous patient underwent laparoscopic cystectomy. Histological examination revealed a borderline mucinous ovarian tumor. No additional treatment was prescribed. Two years later, the patient relapsed with a malignant mucinous ovarian carcinoma. She underwent surgical resection and staging, including hysterectomy, bilateral adnexectomy, omentectomy, and pelvic and paraaortic lymphadenectomy, and platinum-based chemotherapy. Conclusion(s): Recurrence in the form of invasive ovarian carcinoma may occur in the same ovary after cystectomy in cases of borderline mucinous ovarian tumor. An approach combining systematic unilateral salpingo-oophorectomy and strict monitoring is preferable to simple cystectomy. Such treatment enables preservation of reproductive potential and reduces the risk of developing invasive carcinoma. Objective: To report on ovarian cancer development after cystectomy for a borderline mucinous ovarian tumor. Design: Case report. Setting: A French comprehensive cancer center. Patient(s): One patient who developed recurrence in the form of an invasive ovarian carcinoma after simple cystectomy for a borderline mucinous ovarian tumor Intervention (s):. Simple cystectomy Main outcome Measure (s):. Clinical outcome Result (s):.. A 22-year-old nulliparous patient underwent laparoscopic cystectomy Histological examination revealed a borderline mucinous ovarian Tumors. No additional treatment was prescribed. Two years later, the patient relapsed with a malignant mucinous ovarian. She underwent surgical resection and staging, including hysterectomy, bilateral adnexectomy, omentectomy, and pelvic and paraaortic lymphadenectomy, and platinum-based chemotherapy. (s): Recurrence in the form of invasive ovarian carcinoma may occur in the same ovary after cystectomy in cases of b单词orderline mucinous ovarian tumor. An approach combining systematic unilateral salpingo-oophorectomy and strict monitoring is preferable to simple cystectomy. such treatment enabling preservation of reproductive potential and reduces the risk of developing invasive carcinoma.