Onyx Liquid Embolic System (LES) embolization of highly vascular lesions is becoming more frequently used as an adjuvant therapy prior to surgical resection. The authors present a case of a successful pre-operative embolization of a glomus jugulare tumor using Onyx LES. The patient returned for scheduled operative resection one week later. Immediately following the surgery, the patient experienced new onset left hemiplegia. Full radiological workup revealed a fragment of Onyx LES occluding the middle cerebral artery (MCA). All indications are that the fragment became dislodged during the operation. To our knowledge, there have been no other reported cases where complications of tumor embolization with Onyx LES occurred during surgical resection.