Deep infiltrating endometriosis is an important gynecologic disease that may develop during the reproductive years and is responsible for severe pelvic pain. Deep pelvic endometriosis can affect the retrocervical region, uterosacral ligament, rectum, rectovaginal septum, vagina, urinary tract, and other extraperitoneal pelvic sites. Surgery remains the best therapeutic treatment for affected patients and an accurate preoperative evaluation of the extension of endometriotic lesions is essential for a successful outcome. However, many atypical locations for deep pelvic endometriosis exist although still lesser known to both gynecologists and radiologists such as endometriosis of the round ligaments of the uterus (RLUs). In this article, we review embryology and anatomy of the RLUs as well clinical characteristics associated with these endometriotic locations. In addition, we describe magnetic resonance (MR) imaging protocol, normal MR imaging appearances of the RLUs and the most common abnormal findings of endometriotic involvement of these ligaments at MR imaging. Radiologists should always keep in mind the RLUs as a possible site of deep pelvic endometriosis localization and should not forget to carefully look for them on MR images.