This paper focused on malaria epidemic in Ryukyu Islands during World War II with special reference to Yaeyama Islands to prove whether malaria outbreak in Yaeyama in 1945 was unusual, by reanalyzing published data by various researchers and unpublished documents of the U.S. military Government that occupied Ryukyu Islands from 1945 to 1972. The following results were obtained: 1) Outbreak of malaria in the Ryukyu Islands in a period from 1945 to 1947 was caused by great alteration of biologic balances due to military operations by Japanese Army. 2) Compared with those in Miyako and Okinawa Islands, fatality from malaria in Yaeyama in 1945 was extraordinarily high. 3) Forced evacuation of the inhabitants to malaria endemic areas by the Japanese Army caused exceptionally high incidence, mortality and fatality in Yaeyama. 4) Of species of malaria parasites, malignant P, falciparum was predominant in Yeayama. P. vivax was preponderant both in Miyako and Okinawa Islands . 5) In Okinawa Islands, intensive mosquito control measures were initiated by the US Army when they landed the Island in April 1945. But in Miyako and Yaeyama Islands, only partial chemotherapy was administered, not full scale mosquito control activities . In conclusion, unusual outbreak of malaria epidemic in Yaeyama in 1945 was mostly attributed to the forced evacuation of the inhabitants to malaria endemic areas by the Japanese Army.
