Setae located on the abdomen and scape of both sexes of adult Aedes aegypti (L.) as well as selected thoracic and abdominal setae of pupae were found, using transmission electron microscopic techniques, to have the structural features of cuticular mechanosensilla. Each sensillum is innervated by one neuron, the dendrite of which terminates at the setal base or in the setal shaft as a tubular body, a parallel arrangement of microtubules within an electron dense material. These results coupled with those from previous light and electron microscopic studies indicate that all of the setae on the bodies of larval, pupal, and adult Ae. aegypti are probably mechanosensory. The likely roles of these sensilla in the mosquitoes' behavior are discussed.