Ecdysone agonists are hormonally active insect growth regulators that disrupt development of pest insects and have potential for development as insecticides. Their effects have been particularly well-studied in Lepidoptera and Coleoptera, but significantly less is known about their effects on dipterans, particularly aquatic species. The potency of three ecdysone agonists on larvae of 3 mosquito species, Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus, was examined. Anopheles gambiae was the most susceptible species and Ae. aegypti was the most resistant species to the effects of the three compounds tested. Potency, in descending order, was RH-2485 > RH-5992 > RH-5849. Dose-response relationships were determined for the three agonists; RH-2485 was found to be the most effective endocrine disruptor against all three species. The observed biological effects of these compounds were similar to those reported for other insects, and mosquitoes initiated molting and apolysis but did not complete a molt. In some cases, mosquito larvae synthesized a new cuticle that appeared to be normally sclerotized but the larvae failed to ecdyse and shed the exuvium. These compounds may prove to be valuable insect growth regulators for control of mosquitoes to decrease the frequency of pathogen transmission to humans. Prospects for using these compounds to control mosquitoes in the field are discussed, along with possible impacts on non-target arthropods in mosquito habitats.