This study evaluated the efficacy of methoprene, a widely used juvenile hormone mimic, formulated as 30-day slow release Altosid^® pellets, at controlling mosquitoes in underground storm water drainage catch basins. Data from applications to ¼-sized cement catch basins in the laboratory, field observations from treated and untreated basins, and an experiment that confined mosquito larvae in floating emergence jars in catch basins showed that methoprene effectively controlled mosquitoes for a month under field conditions and substantially longer under laboratory conditions when applied at a dose of 3.5-g pellets per average-sized catch basin.