The occurrence of larvae of two potential vectors of West Nile virus, Culex nigripalpus and Culex quinquefasciatus, was examined in the Florida Keys. About half of the aquatic habitats examined contained larvae of either one or both of the species. Culex quinquefasciatus was the most frequently encountered species, whereas only 9% of habitats sampled contained Culex nigripalpus. Over half of those samples that contained Culex nigripalpus also contained Culex quinquefasciatus. The two species utilize similar larval habitats in the Florida Keys, Monroe County, Florida, USA.