ABSTRACTIntroduction: We describe the ultrasonographic findings of sciatic nerve endometriosis. Methods: Two premenopausal women with catamenial sciatica symptoms were examined, the first without a history of endometriosis, the second with previously confirmed endometriosis of the ovary. Ultrasonography, extending from the sciatic notch to the level of the ischial tuberosity showed that the sciatic nerve was “engulfed” in a large, perineural, hypoechogenic, inhomogeneous lesion with an irregular contour corresponding to an endometrioma. The nerve was enlarged, but it was discernible within the lesion, except at its most cranial part. MRI of the pelvis showed intrapelvic extension in both patients. Results: The first patient was treated with a gonadotropin‐releasing hormone agonist, leading to complete morphological regression and normalization of nerve structure, parallel with symptomatic resolution. Conclusions: These cases illustrate that ultrasound is a feasible imaging modality for sciatic nerve endometriosis that may even be used to monitor morphological regression of endometrial tissue during treatment. Muscle Nerve 54: 500–505, 2016