The aim of this study was to estimate the prevalence of multiple sclerosis (MS) in Korea through a nationwide survey. We estimated the prevalence of MS in Korea using several sources collected between 2000 and 2005: verified cases from 38 major referral hospitals across the nation, the National Health Insurance (NHI) payment request data from NHI Corporation of Korea, and the national mortality dataset from Statistics Korea. We established a network of neurologists from 38 major referral hospitals and performed a nationwide hospital survey for MS cases. The diagnoses of MS were validated according to the McDonald criteria. The diagnostic validity of each hospital was evaluated from hospital survey data to reduce the uncertainty of NHI data and was applied to estimate the prevalence using novel statistical methods. The estimated numbers of MS cases in Korea through 2 different statistical methods which adjust NHI data by the diagnostic validity of each hospital were very similar: 1,681 (95% confidence interval CI 1,490-1,902) by the stratification method and 1,640 (95% CI 1,402-1,789) by the linear regression method. The crude MS prevalence was 3.5-3.6 cases per 100,000 individuals. The estimated female-to-male ratio was 1.26. This study is the first nationwide survey for the prevalence of MS in Korea utilizing a national database in complementary way. We found an increase in the prevalence of MS that is consistent with reports from neighboring Asian countries.