This report describes a cluster of 11 soldiers with vivax malaria among U.S. military personnel who trained at Dagmar North training area, near the demilitarized zone (DMZ), in the Republic of Korea (ROK) in 2015. Two cases were diagnosed in the ROK in 2015, one of whom subsequently experienced a relapse, and nine other cases were diagnosed in 2016, 8-11 months after the soldiers had returned to the U.S. Vivax malaria poses a health threat to U.S. Forces Korea operating near the DMZ in the ROK. Continuing and enhanced focus on force health protection measures in endemic zones is warranted.