The effects of azadirachtin A added to the sucrose diet of the adult females on the mortality, oviposition, and hatching of the sand ßy vector of American visceral leishmaniasis Lutzomyia longipalpis (Lutz & Neiva, 1912) were investigated. Concentrations of 0.1, 1.0, and 10.0 g/mg of azadirachtin signiÞcantly increased insect mortality in comparison with control insects. The same dose also signiÞcantly reduced oviposition but not hatching. After a long development period, signiÞcantly fewer adult insects were obtained from eggs hatching by azadirachtin-treated females in a doseÐ response manner. These results indicate that azadirachtin is a potent sterilizer that could be used against the development of Lu. longipalpis populations and as a tool for studying physiological and biochemical processes in phlebotomine species.