A prevalence study of chronic inflammatory demyelinating polyneuropathy (CIDP) was performed in New South Wales (NSW), Australia, with a prevalence day of August 6, 1996, which coincided with a national census. The population of NSW was 5,995,544, and the crude prevalence of CIDP was 1.9 per 100,000 population. It was higher in male patients than in female patients, and the age-specific prevalence reached a maximum of 6.7 per 100,000 population in the 70- to 79-year-old age group. The prevalence in the city of Newcastle, with a population of 448,663, was 2.0 per 100,000 population and is representative of the whole of NSW. The estimated crude annual incidence was 0.15 per 100,000 population. The mean age of onset was 47.6 years (median, 53.5 years), 51% of patients had a relapsing-remitting course, the mean duration on prevalence day was 7.1 years (median, 5 years), and 87% of patients were able to walk without walking aids or other assistance.