Insecticides are the most common strategy used for the management of mosquitoes. Changes in ambient temperature can alter the toxicity of insecticides to ectothermic organisms. Studies show organophosphate insecticides exhibit a positive correlation between ambient temperature and mortality for many insect species, and carbamate insecticides exhibit a slightly negative correlation between ambient temperature and mortality. Pyrethroid insecticides exhibit a distinctly negative correlation between increasing ambient temperature and mortality for insects. However, this relationship has not been systematically studied for adult mosquitoes. Therefore, we examined the influence of temperature on the susceptibility of adult Aedes aegypti L. (Diptera: Culicidae) when exposed to permethrin. The median lethal concentration, LC₅₀, was estimated for adult Ae. aegypti when exposed to eight concentrations of permethrin (ranging from 0.06–0.58 ng/cm²) at each of the following temperatures—16, 23, 26, 30, 32, and 34°C—for 24 h in bottle assays. The estimated LC₅₀ for each temperature was 0.26, 0.36, 0.36, 0.45, 0.27, and 0.31 ng/cm², respectively. Results indicated a negative correlation between temperature and mortality from 16 to 30°C, a positive correlation between temperature and mortality from 30 to 32°C, and a negative correlation between temperature and mortality from 32 to 34°C. If mosquito populations are expanding in space and time because of increased ambient temperatures and cannot be managed as effectively with pyrethroids, the spread of mosquito-borne diseases may pose considerable additional risk to public health.