Uterine fibroids, also known as leiomyomas, represent the most common benign tumors of the female genital tract. Submucosal leiomyomas are classified into three grades: G0, GI, GII according to the degree of their intramural proportion. A recently developed technique enables the preparation of G1 and G2 leiomyomas for their subsequent successful resection in a second step. The OPPIuM (office preparation of partially intramural leiomyomas) technique aims to downgrade type I and II leiomyomas, in order to facilitate a subsequent easier and safer resectoscopy. Hysteroscopic resection of large GI or GII submucosal fibroids is a complex procedure. OPPIuM technique has been invented and seems to achieve the downgrading of these types of leiomyomas in approximately 93% of cases, without any significant surgical complications or the need of hormonal agents' administration. In this way, the safer and quicker subsequent complete myomectomy is facilitated.