Brivudin is an oral antiviral agent used to treat herpes zoster infections. Common side effects of brivudin include nausea and headache. This report describes delirium in a patient who used brivudin for herpes zoster treatment, which consequently remitted after drug cessation on the fourth day of medication use. To our knowledge, no such side effect has been reported to date. However, it is important that clinicians who prescribe brivudin are aware that treatment cessation is likely to result in total clinical recovery.