Idiopathic hypertrohpic cranial pachymeningitis is rare, and is essentially a diagnosis of exclusion. A 53-year-old man presented with headache and visual loss in the right eye, first experienced a month earlier. MR images depicted a mass in the right cavernous sinus. At T1-weighted imaging, both the mass and the thickened dura mater present in both fromted lobes were isointense, while at while T2-weighted imaging, the signal intensity of both the mass and the dura mater was low. After the injection of contrast medium, pachymeningeal enhancement was observed. We report the radiologic findings in a case of idiopathic hypertrophic cranial pachymeningitis, confirmed surgically and pathologically.