**3. Epidemiology**

Although originally reported in the Asian population, moyamoya disease has also been reported from Europe and America [1].

In an epidemiological study by Baba et al. [14], MMD was found to have the following characteristics in the Japanese population:


Although the reported incidence of MMS from Washington and California was as low as 0.086 per 100,000 populations generally, in ethnic groups, it was found to be as high as 0.28 per 10,000 populations close to the incidence in Japan [15].

MMS shows a bimodal distribution in the Chinese population with a major peak in the 5–9-year-old group and another peak in the 35–39-year-old group [16]. In the Japanese population, there are two conflicting reports of higher peaks, one in childhood and another in adults [14, 17].
