Background: Paratubal borderline tumors (PBTs) are found incidentally at frozen section or permanant pathology, and are extremely rare. We describe the first case of a paratubal borderline mucinous tumor (PBMT). Case report. A 20-year-old woman was referred with a complex right adnexal mass on pelvic sonogram. She underwent laparoscopic paratubal cyst enucleation. We used an endobag for cyst extraction. Cyst rupture or tearing of the endobag in the laparoscopic field was absent. Frozen section analysis was reported as a borderline mucinous tumor of low malignant potential. Currently, she has had no evidence of disease recurrence after a laparoscopic fertility-sparing staging procedure. Conclusion. A proper preoperative differential diagnosis of an adnexal mass is difficult. Thus, laparoscopy is needed in large or symptomatic cysts. Although growth, torsion and malignancy are rare in paratubal cysts, the possibility of tumor seeding should be excluded with use of an endobag.