Akihiro Tsukadaira1, Tomohiro Sekiguchi1, Takashi Ashida2, Chinatsu Murashita3, Nobuo Itoh3, Mikiko Kobayashi4, Takashi Kagoshima4, Yoshitaka Yamazaki41Department of Internal Medicine, 2Department of Obstetrics and Gynecology, 3Division of Clinical Pathology, Iida Municipal Hospital, Yawatacho 438, Iida, Japan; 4Department of Internal Medicine, Suzaka Prefectural Hospital, Suzaka 1332, Suzaka, JapanAbstract: Certain clinical aspects of vivax malaria are no longer defined as benign. We present a case of vivax malaria with three relapses in a pregnant Japanese woman who had returned to Japan from the Comoros Islands in East Africa. Data on the successful delivery, examination of Duffy-blood group antigen, and microscopic findings of growing stages of Plasmodium vivax are thought to be of considerable interest.Keywords: vivax malaria, Duffy-blood group, pregnancy