An epidemic of Japanese B encephalitis occurred during the summer months of 1949 in Korea. The present report concerns epidemiological, clinical and etiological studies pertaining to this outbreak. Because of the general inaccessibility of previous Korean and Japanese reports, a review of such literature pertaining to prior occurrence of the disease in Korea appears desirable. HISTORY OF PREVIOUS ENCEPHALITIS IN KOREA There are no Public Health records concerning previous instances of Japanese B encephalitis in Korea, because Japanese health authorities did not require that this disease be reported, hence, the only available information on its appearance is in periodic medical publications in the Japanese or Korean language. Prior to 1933 several cases of "summer encephalitis" were reported,1 but only a few are strongly suggestive of Japanese B encephalitis. An outbreak of encephalitis in epidemic proportions occurred in Korea during the summer months of 1934 and 1935 with clinical observations