A case of endometriosis involving the right uterosacral ligament in which nonneoplastic endometrial glands were present in the perineural space is reported. In the past, epithelial invasion of the perineural space was considered evidence of the presence of malignant disease. Rodin and colleagues,2 however, concluded that the perineural space is not a lymphatic space and that involvement may represent extension into the tissue plane of least resistance. Perineural invasion has been reported in benign conditions of the breast, including chronic cystic disease and sclerosing adenosis. It is important that involvement of the perineural space in endometriosis not be interpreted as evidence of malignancy. We believe that involvement of the perineural space in other nonmalignant conditions will be described in the future.