To date, intravenous immunoglobulin (IvIg) has more often been considered as a safe medication. However, with the wider use of IvIg, severe side effects have also been reported to occur in IvIg-treated patients, notably aseptic meningitis. Other neurological complications have more rarely been described in patients receiving IvIg therapy, e.g. stroke or acute encephalopathy. We recently observed a case which is of particular interest, as the patient with steroid-refractory polyarteritis nodosa developed cranial pachymeningitis related to IvIg therapy. To our knowledge, this is the first reported case of cranial pachymeningitis complicating IvIg therapy. Our findings emphasize the importance of recognizing IvIg-related neurological complications in IvIg-treated patients. As cranial pachymeningitis is a fibrosing process, both recognition and management at an early stage are required to prevent definite neurological impairment in patients.