Three cases of idiopathic hypertrophic cranial pachymeningitis are presented. The diagnosis was based on the CT scan or MRI findings (or both) of thickened enhancing dura. In all cases, meningeal biopsies were performed and microscopic findings were compatible with non-specific inflammation. All cases presented with subacute and chronic localized headache. Two cases had associated chronic meningitis. One case presented with a syndrome of multiple cranial nerve involvement (polyneuritis cranialis). Corticosteroids, in the form of prednisolone 60 mg/day, were effective in all cases. Two cases with less severe pachymeningitis received corticosteroids for 2 weeks, then were tapered off in 4 to 6 weeks. A case with extensive lesions needed a long-term low dosage of prednisolone, 5 to 10 mg/day for maintenance therapy. Idiopathic hypertrophic cranial pachymeningitis may be related to the Tolosa-Hunt syndrome, the syndrome of polyneuritis cranialis, and multifocal fibrosclerosis.