Two patients presenting with recurrent multiple cranial neuropathy showed diffuse thickening and gadolinium enhancement of the dura mater on brain MRI. Both had anti-HTLV-I antibodies in serum. A quantitative polymerase chain reaction study of the peripheral blood disclosed that the HTLV-I proviral DNA loads increased considerably in one case and moderately in the other. Both showed a spontaneous proliferation of peripheral blood lymphocytes as well as an increase in helper/inducer T cells. Neither had any other underlying infections or autoimmune diseases. Thus it is possible that hypertrophic pachymeningitis developed as a result of multiorgan involvement of HTLV-I infection in these patients.