Five study sites within three of seven provinces along the Thailand-Cambodia border were selected in areas where there were known to be many migrant workers and close by areas where P. falciparum resistance to artemisinins has been documented; three sites recruited for Cambodian migrants (one each in Chantaburi, Trat, and Sa Kaeo provinces) and another two sites for Myanmar migrants (both in Trat). The survey was conducted from June to September 2009. Figure 1 shows the five locations in Thailand where surveys were conducted as part of joint Cambodia Thailand containment operations.