Air conditioning of dwellings in developing countries is currently rather rare, but increasing personal income is expected to change that. This study examined the potential energy demand for cooling in the 50 most populous metropolitan areas of the world, and assessed the incremental demand in developing countries that this would create on top of the current energy demand due to heating. The analysis used local cooling and heating degree-day data. The main results are as follows: (1) Most of the largest metropolitan areas are in developing countries (38 out of 50), and most of them, in turn, are in warm to hot climates. (2) All but two of the top 30 metropolitan areas in terms of cooling degree days are in developing countries, (3) The potential cooling demands are greater than heating demands in most of the metropolitan areas that are in developing countries (24 out of 38). The main implication of these findings is that increasing personal income is likely to lead to an unprecedented increase in energy demand in many developing countries. For example, the potential cooling demand in metropolitan Mumbai is about 24% of the demand for the entire United States. (C) 2008 Elsevier Ltd. All rights reserved.