Anesthesiologists commonly use opioids for pain control in the operating room and postanesthesia care unit, and are constantly vigilant in looking for possible adverse outcomes. Therefore, common complications such as nausea, vomiting, and pruritus are well known. However, neurologic complications after opioid administration are relatively rare except for reduced consciousness, for example drowsiness or sedation. We recently experienced a case in which a 73-year-old woman presented predominantly vertical nystagmus as a neurological complication after epidural administration of fentanyl. A few previous reports on opioids as causative agents for nystagmus have all after use of epidural morphine, and there are yet no publications reporting epidural fentanyl as the cause of nystagmus. Physicians should keep in mind that epidural fentanyl could cause the nystagmus as a neurological complication even though it is used within conventional dosage ranges, although this is very rare. Also, when a patient develops nystagmus after epidural fentanyl, it could be a benign side effect caused by epidural fentanyl as we have experienced, but it could also be a sign of serious central nervous system lesions especially in patients with underlying risk factors such as old age, diabetes mellitus, hypertension, and cerebrovascular disease, and thus special attention should be paid to this.