Malaria transmission in the United States was largely eliminated during the mid-20th century; however, sporadic cases of locally acquired mosquito-transmitted malaria continue to occur. Since 1997, four separate probable mosquito-transmitted malaria outbreaks have been reported to CDC, including one from Virginia. This report describes the investigation of two cases of Plasmodium vivax malaria that occurred in northern Virginia in August 2002, and underscores the need for clinicians to consider the possibility of malaria in patients with fever of unknown origin.