Hilmilin (diflubenzuron), an insect growth regulator, was tested for efficacy against Anopheles stephensi, Anopheles culicifacies, Aedes aegypti, and Culex quinquefasciatus in the laboratory and in field conditions. Fifty percent and 90% lethal concentrations (LC₅₀ and LC₉₀) of Hilmilin formulations were determined by exposing early 4th-stage larvae to serial dilutions of the formulation, and data were subjected to log probit analysis. Two doses (0.004 and 0.008 g/m²) were applied in different breeding habitats of mosquitoes with the help of stirrup pumps. Percent inhibition of adult emergence was compared according to a previously described procedure. Laboratory results revealed that both 25WP (wettable powder) and 22SL (semiliquid) formulations showed more or less the same degree of efficacy against tested mosquito species (P < 0.05). Of 4 species tested, An. stephensi was more susceptible, followed by An. culicifacies, Ae. aegypti, and Cx. quinquefasciatus. One hundred percent inhibition of adult emergence was observed at a dose of 0.0125 ppm (25WP and 22SL) against all mosquitoes tested in the laboratory. Both formulations showed almost similar effect when applied in the field at doses of 0.004 and 0.008 g/m² in their respective preferential breeding habitats. However, the effect was more pronounced at a higher concentration (0.008 g/m²) against all species of mosquitoes. Hilmilin at a dose of 0.008 g/m² can be used to contain mosquito breeding in stone quarries, pools, cement tanks, unused wells, unused coolers, and irrigation channels.