Methemoglobinemia is a condition in which methemoglobin levels in the blood increase. Methemoglobin lacks oxygen-binding ability, resulting in oxygen deprivation in tissues. This high level of methemoglobin in the blood presents as a severely worsening condition. Herein, we report a case of methemoglobinemia caused by the administration of 3% prilocaine hydrochloride containing 0.03 IU/mL feripressin as a local anesthetic during orthognathic surgery. Following drug administration, the patient's atrial oxygen saturation (SpO