The larval stage of Amblyomma cajennense is redescribed, using optical and scanning electron microscopy. Larvae were obtained in the laboratory from an engorged A. cajennense female which had been collected on a horse in the municipality of Itaguai, State of Rio de Janeiro, Brazil. The chaetotaxy of the idiosoma, palps and Haller s organ, the campaniform sensillum on the fifth festoon, as well as other structures, are described for the first time. The nomenclature employed in the chaetotaxy of the palps and Haller s organ is discussed.