We report a case of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) in a middle-aged patient with hepatitis C virus (HCV) infection. A 49-year-old man presented chronic progressive distal motor weakness and sensory disturbances. Laboratory findings indicated chronic liver dysfunction due to HCV infection, transient positive serum cryoglobulinemia and marked decreased motor and sensory conduction velocities in electrodiagnosis. Lumbar MRI showed marked hypertrophy of the bilateral lumbar radicular nerve roots. Steroid treatment, not IVIg, improved neurological manifestation of this patient, but the serum HCV-RNA level was extremely increased after this treatment. Choice of treatment for patients suffered from CIDP associated with HCV infection is still controversial. Newly discovered patients with HCV infection are increased in Japan in number according to the routine check their anti-HCV antibodies. It is important to monitor carefully the serum HCV-RNA level in CIDP patients associated with HCV infection when steroid treatment is initiated.