Endometriosis that involves nerves is rare and usually occurs in the pelvis. We describe a case of extra-pelvic endometriosis that involved the superior gluteal nerve. The patient presented with ill-defined buttock and thigh pain and a Trendelenberg gait. MRI demonstrated atrophic changes in the gluteus minimus, gluteus medius and tensor fascia lata muscles indicating involvement of the superior gluteal nerve. MRI showed a mass in the line of the superior gluteal nerve. The mass was hyperintense on STIR and T1-weighted images and did not enhance after intravenous contrast although surrounding edema did enhance. Histological examination of material obtained at open biopsy showed endometriosis. The patient was commenced on hormonal treatment to suppress ovarian activity.