A 65-year-old woman underwent surgical treatment of an unruptured aneurysm in the left middle cerebral artery. Surgical craniotomy using arachnoid plasty with a fibrin sealant was completed without incident, but abrupt neurological deterioration occurred on the 9th postoperative day. Antibiotic treatment was given, but the symptoms did not resolve. Neuroimaging and physical findings indicated allergic reaction rather than infectious process. Therefore, systemic steroids were administered that resulted in dramatic resolution of symptoms. Nine months later, lymphocyte stimulation test of materials used in arachnoid plasty revealed positive response to a component of the combination pair in fibrin glue. The fibrin sealant placement method is a widely accepted and familiar technique, but surgeons should anticipate possible allergic reactions such as those observed in the present case.