In their epidemiological studies on the epidemic of Japanese B Encephalitis that broke out in Tottori Prefecture during past 15 years (1950-1964), the authors obtained the following results.
1) Every year's morbidity rate except 1954 in Tottori Prefecture was higher than that in all Japan.
2) As for the season of prevalence, the end of August or the beginning of September was a peak of prevalence.
3) In the next year of a high epidemic year, there was tendency that the peak of prevalence expressed as median was later coming than that of the former year.
4) As for the district of prevalence, the morbidity rate of Sakaiminato City is the smallest in Tottori Prefecture during past 15 years.
5) As for the sex, male morbidity rate was higher than female one.
6) Concerning age, rate of morbidity in children below 10 years of age has been decreased, and that in people above 60 years of age has been increased during past 5 years.