We report a case of diffuse endometrial squamous metaplasia found after in a resectoscopic myomectomy specimen. A 35-year-old woman underwent an office hysteroscopy that showed a submucosal leiomyoma. After pharmacologic treatment with a GnRH gonadotropin-releasing hormone agonists (GnRHa) leuprolide acetate, the patient underwent a resectoscopic myomectomy. Histologic examination showed fragments of myometrial tissue with the foci of endometrial glands with diffuse features of squamous metaplasia; in part classical, mature type; and in part immature type, and the so-called "morula type." Presence of endometrial squamous metaplasia in the endometrium may produce dramatic histologic changes on biopsies and sometimes it may be difficult to distinguish it from primitive primary carcinomas of nonendometrioid histology, representing therefore, a potential diagnostic pitfall. GnRHa therapy could play a possible role in the onset of squamous metaplasia. So the pathologist and gynecologist must take into account this possible metaplastic change for a correct clinicopathologic assessment and to avoid overtreatment.