Objectives: Dengue fever is a human health and life-threatening mosquito-borne disease in tropical regions of the world, and is prevalent in southeast Asia, Central America, South America, and the western Pacific region. Without effective treatment, insecticide spray to control the vector has been the top priority in attempts to prevent dengue transmission. This study evaluated the cost utility of insecticide spray in the early stage of a dengue outbreak in Kaohsiung. These results will provide suggestions for controlling dengue fever with limited resources and lowering the epidemic size and social burden of dengue fever. Methods: Decision-making and sensitivity analysis were performed with Treeage Pro 2011. The incidence of dengue fever with incorporation of the following factors into a decision tree: with or without early insecticide spraying; manpower; material expenditures; medical expenses of patients; and DALYs. Results: A cost utility analysis indicated that spontaneous spraying of insecticide and environmental clearance indoors and outdoors within a radius of 100 meters of the case premises was a better decision than no spray control. Specifically, it would cost 957.16 NTD/person and 0.0144 DALYs lost per 1 million population with an incidence of 0.0536 with insecticide spray. In contrast, it would cost 1575.24 NTD/person with and 0.0257 DALYs lost per 1 million population with an incidence of 0.0954 without insecticide spray. The early spray approach had good cost utility, with an incidence ranging from 0.058-0.091. Conclusions: This study defined a suitable incidence interval with cost utility with respect to dengue fever control using early insecticide spraying. Despite the cumulative incidence beyond this range, other control strategies may cooperate with insecticide spraying to reduce the outbreak and severity of dengue (hemorrhagic) fever. [ABSTRACT FROM AUTHOR]