Characterization of insecticide resistance provides data on the evolutionary processes involved in the adaptation of insects to environmental changes. Studying the dominance status and resistance level represents a great interest, in terms of understanding resistance evolution in the Þeld to eventually adapt vector control. Resistance and dominance levels conferred by the G119S mutation of acetylcholinesterase (ace-1R) of the mosquito Anopheles gambiae s.s. (Diptera: Culicidae) were studied for various insecticides belonging to different classes, using strains sharing the same genetic background. Our survey shows that the homozygote resistant strain AcerKis displayed a very high resistance level to various carbamates (range 3,000- to 5,000-fold) compared with that of various organophosphates (range 12- to 30-fold). Furthermore, the dominance status varied between semirecessivity with fenitrothion and chlorpyrifos methyl insecticides to semidominance with temephos, carbosulfan, and propoxur. These results indicate that this resistance mechanism could spread rapidly in the Þeld and then compromise the use of organophosphate and carbamate compounds in public health. This study underlines the necessity to monitor the ace-1R mutation in natural populations before planning and implementing malaria control programs based on the use of these insecticides.