In the United States, malaria transmission was eliminated in the 1940s, and malaria eradication was certified in 1970 (1). Since then, 60 small localized outbreaks of probable mosquito-transmitted malaria have been reported to CDC (2-6). Before 1995, the number of imported malaria cases reported to the Suffolk County (New York) Department of Health Services ranged from zero to eight per year. Since 1995, seven to 17 cases per year have been reported. In all of these cases, a history of residing in or traveling to an area with endemic malaria outside the United States was confirmed. This report describes the investigation of two cases of Plasmodium vivax malaria that occurred in Suffolk County in August 1999; the patients had no history of travel outside of the United States.