A nationwide survey was carried out to estimate the frequency and distribution of Vogt-Koyanagi-Harada disease in Japan. A questionnaire was mailed to the Departments of Ophthalmology in hospitals with 200 or more beds. Responses were received from 489 out of 1,077 institutions, or 45.5%. The annual prevalence was estimated to be 15.5 per million and the incidence was 6.5 per million, based on the number of reported cases and the response rate per prefecture. It was estimated that 1,800 patients were treated for this disease annually and that there were about 800 new cases each year. Geographical distribution showed no special characteristics such as those seen with Behçet's disease. The results of the analysis of 1,833 reported cases showed that females were slightly more often affected than males. For both male and female patients, the age distribution on the first visit showed a peak in the fifth decade and a median age of 42.3 years.