Treatment of Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) is a challenge because disease may generate important disability in patients including young adults. Randomized trials showed that corticosteroids, plasma exchanges and intravenous immunoglobulin (IVIg) can reduce impairment on a short term period but the treatment of a chronic disease doesn't agree with it. Corticosteroids and IVIg are the first line CIDP treatments. No study permits to demonstrate the superiority of one treatment to the other. Long term adverse effects of corticosteroids and IVIg cost are the respective limitation of their use. The investigators scheduled to recruit 40 CIDP patients in 23 French centres to receive either 0,8mg/kg/day of prednisone progressively tapered over 6 months or a monthly 2g/kg cure of IVIg during 6 months. Patients will be followed during 6 months after the treatment.