Vaginal endometriosis is often associated with the posterior infiltrative involvement of the uterosacral ligaments, torus uterinum, rectovaginal septum, rectum, and parametrium. Diagnosing this disease location during a preoperative workup is crucial for several reasons: (1) Patients counseling patients on the surgical procedure and the postoperative period and (2) planning the surgery, including the risk of digestive derivation with a stoma and with concomitant rectum involvement. Vaginal endometriosis diagnosis can be challenging in imaging, and it is a location where physical examination is highly specific for assessing the presence and the extent of disease but is associated with low sensitivity. The posterior vaginal fornix is the primary site for vaginal involvement, often arising from the inferior extension of a retrocervical lesion. The vaginal involvement ultrasound (US) diagnostic is very subtle and requires a high level of expertise. On MRI, vaginal involvement is reflected by the presence of a hyposignal T2 nodule under the reflection of the peritoneum behind the uterine cervix.