Background: Fetus-in-fetu (FIF) is a rare, congenital soft tissue mass typically occurring retroperitoneally in neonates younger than 18 months. We present a 13-year-old girl with an ovarian FIF occurrence and subsequent residual regrowth after resection.

Case: A 13-year-old girl presented with abdominal pain and was found to have a 19-cm, complex, right adnexal mass. Preoperative tumor markers were normal and risk assessment favored a benign process. She underwent open ovarian cystectomy with pathology showing FIF. Nine months later, she had a recurrence of her ovarian mass and underwent right oophorectomy, with FIF on pathology.

Summary and Conclusion: In patients in whom FIF is discovered within the ovary, consider postoperative surveillance, because of the risk of recurrence or residual disease.

背景：胎中胎儿 (FIF) 是一种罕见的先天性软组织肿块，通常发生在小于 18 个月的新生儿的腹膜后。我们介绍了一名 13 岁的女孩，其卵巢 FIF 发生并随后在切除后残留再生。

病例：一名 13 岁女孩因腹痛就诊，发现右侧附件有一个 19 厘米的复杂肿块。术前肿瘤标志物是正常的，风险评估有利于良性过程。她接受了开放性卵巢囊肿切除术，病理显示 FIF。九个月后，她的卵巢肿块复发并接受了右侧卵巢切除术，病理学检查为 FIF。

总结和结论：对于在卵巢内发现 FIF 的患者，考虑术后监测，因为存在复发或残留疾病的风险。