Moyamoya disease is an idiopathic vascular disorder of the intracranial arteries. Ring finger 213 (RNF213) was previously identified as the strongest susceptibility gene for moyamoya disease in East Asian people by a genome-wide linkage analysis and exome analysis. The coding variant p.R4810K in RNF213 was strongly associated with moyamoya disease in the Japanese (odds ratio: 338.94, p = 1.05 × 10⁻¹⁰⁰) and Korean (odds ratio: 135.63, p = 7.59 × 10⁻²⁷) populations, and much less strongly associated in the Chinese population (odds ratio: 14.70, p = 2.63 × 10⁻⁵). The present study investigated the distribution of variant p.R4810K in RNF213 in 2,508 participants from East and Southeast Asian countries using a TaqMan probe. p.R4810K was detected at an allele frequency of about 1.00% in 4 of 11 investigated locations in China. In contrast, p.R4810K was detected homogeneously at relatively high frequencies of 1.00-1.72% in all investigated locations in Korea and Japan, including Okinawa. p.R4810K was not detected in Southeast Asian populations. The population susceptible to moyamoya disease was estimated to be 16.16 million people in East Asian countries, including 11.41 million Chinese, 1.36 million Korean, and 3.39 million Japanese people. The number of patients with moyamoya disease, which was estimated at approximately one per 300 carriers of p.R4810K, was considered to be 53,800 in East Asian populations.