The distribution and ecological 'preferences', in the Nearctic and Neotropical regions, of the prominent, pathogen-carrying tick Amblyomma cajennense (Fabricius) were reviewed, on the basis of the published literature, satellite imagery, and the examination of several tick collections. The tick has been collected from the southern U.S.A. (Texas and Florida) to northern Argentina, but is probably absent from Uruguay and southern Brazil (the few records of the species in these areas probably represent mis-identifications). The ecological conditions prevailing in the areas where the tick has been reported were characterized using remotely sensed data on temperature and vegetation stress (as indicated by the normalized derived vegetation index, or NVDI). In Mexico and the U.S.A., the species is found in areas where the mean temperature is around 13-16 degrees C and the NVDI is high. South of Venezuela, however, the tick is only common in zones where the mean temperature is 18-20 degrees C and the NVDI is again high. It is relatively low mean temperatures and differences in the seasonal patterns of rainfall that seem to limit the tick's colonization of areas to the north of its current distribution. Low temperatures also seem to be keeping the tick out of mountainous areas, such as the Sierra Madre in Mexico and the pre-Andean hills in Argentina. The southern distribution of A. cajennense is mainly restricted by relatively low temperatures and not by low humidity.