We report on a 48-year-old man with idiopathic hypertrophic cranial pachymeningitis (IHCP) manifesting headache, facial pain, and tongue pain with unilateral atrophy, dysarthria, and dysphagia. Although steroid therapy ameliorated these symptoms, they recurred after he developed steroid-induced diabetes mellitus. We treated the patient by lymphocytapheresis (LCP), which resulted in an improvement of his symptoms, a reduction in the CD4 lymphocyte population, a reduction of the CD4/CD8 ratio, and a reduced thickening of the dura mater that lasted for more than 14 months. Results presented here suggest that LCP can be effective in the treatment of IHCP.