The cost-effectiveness of lambdacyhalothrin-treated nets in comparison with conventional DDT spraying for malaria control among migrant populations was evaluated in a malaria hyperendemic area along the Thai-Myanmar border. Ten hamlets of 243 houses with 948 inhabitants were given only treated nets. Twelve hamlets of 294 houses and 1,315 population were in the DDT area, and another 6 hamlets with 171 houses and 695 inhabitants were in the non–DDT-treated area. The impregnated net program was most cost-effective (US$1.54 per 1 case of prevented malaria). Spraying with DDT was more cost-effective than malaria surveillance alone ($1.87 versus $2.50 per 1 case of prevented malaria). These data suggest that personal protection measures with insecticide-impregnated mosquito net are justified in their use to control malaria in highly malaria-endemic areas in western Thailand.