The influence of the microsporidium Edhazardia aedis (Kudo) on the survival and reproduction of its mosquito host, Aedes aegypti (L.), was studied in the laboratory. Survival, fecundity, egg hatch, and percentage of emergence for 4 gonotrophic cycles were compared for control and infected mosquitoes. Control females oviposited an average of 123.1 eggs over 4 gonotrophic cycles, 86.1% of which hatched, whereas infected females laid an average of 38.0 eggs with a 69.3% hatch. Emergence in progeny of infected female Ae. aegypti was significantly less than for control mosquitoes in all gonotrophic cycles. The reproductive capacity (Ro) for control and infected adults was 168.4 and 4.1, respectively, representing a decrease of 98.2%. Overall infection levels in progeny of infected females was 95.7%, of which 46.6% were lethal, larval infections. Infected female survivors were capable of initiating infections in F2 progeny. Wing length, often used as an indicator of fitness, was not significantly different between infected and control adults.