Background: Cryopreservation of oocytes is an efficient method of fertility preservation (FP) that can be applied in women suffering from gynecologic conditions that menace their reproductive future. Collection of oocytes becomes challenging in some scenarios, like the possibility of an ovarian cancer, the "ex-vivo" harvest of oocytes for FP, aspirating follicles directly from the ovarian specimen already excised by laparotomy or laparoscopy and it is an option for these cases. Case Presentation: In the present case report, the case of a patient with an adnexal mass suspected to be a recurrent teratoma was described who referred to our Assisted Reproduction Unit in Hospital Quironsalud Malaga for FP counseling. After controlled ovarian hyperstimulation, followed by laparoscopic abdominal examination and oophorectomy, an ex-vivo follicular aspiration for oocyte retrieval was performed on the specimen, using a standard ultrasound-guided procedure to ease and improve the process. All the follicles were aspirated and 5 metaphase II oocytes were obtained. Conclusion: This is to our knowledge, the first communication describing the ex-vivo ovarian aspiration of mature oocytes for FP using standard ultrasound guidance. Although this ultrasound guidance is not completely necessary, as other authors demonstrated previously, such a procedure permitted an easy and complete harvest of oocytes in a rare tumor with bizarre cystic formations, which made follicle recognition very difficult.