The effects of azadirachtin A added to the standard diet on the development, mortality, and metamorphosis of Lutzomyia longipalpis Lutz & Neiva, 1912 were studied. Concentrations of 0.1, 1.0, and 10.0 g of azadirachtin/mg of diet signiÞcantly increased larval mortality in comparison with nontreated insects. Concentrations 0.1 and 1.0 g blocked the molt of larvae, which remained as third instars until the end of the experiment.The10 g/mgconcentration resulted in greater molt inhibition. In this group, all insects stopped their development as second instars. Simultaneous addition of ecdysone (1 g/mg) to the standard diet containing azadirachtin counteracted the effects of azadirachtin on mortality and inhibition of ecdysis. These results indicate that azadirachtin is a potent growth inhibitor of L. longipalpis.