The threat from dengue has grown dramatically. The World Health organization estimates that there may be up to 100 million thousands die because of dengue each year. Controlling mosquitoes is the only available dengue prevention strategy, but dengue control activities tend to be limited to reponses to outbreaks. This report documents a promising, feasible, low-cost measure for controlling Aedes egypti mosquitoes, the primary household-associated dengue vector. The intervention involved encouraging local communities in Cambodia and the Lao People's Democratic Republic to use small fish called guppies to devour mosquito larvae in household water containers; this was accompanied by intense communication activities. The result was significant reductions in the number of containers with mosquito larvae and of mosquito pupae per person. The approach is being considered for expansion to other areas of Cambodia and the Lao People's Democratic Republic and is also being taken to countries in the South Pacific with a view to assessing its wider suitability.