The first dengue viruses were isolated from soldiers who became ill in Calcutta, India, New Guinea, and Hawaii. The viruses from India, Hawaii, and one strain from New Guinea were antigenically similar, whereas three other strains from New Guinea appeared to be different. Many early workers suspected that dengue viruses were transmitted by mosquitoes, but actual transmission was first documented by H. Graham in 1903. The first epidemics of dengue-like illness reported in the medical literature occurred almost simultaneously in 1779 in Cairo and Batavia, Indonesia. Historically, dengue was described as an adult disease of the expatriate communities in tropical endemic areas of Asia and was not commonly observed or recognized in the local population. The impact of epidemic dengue on tourism is difficult to measure, but any decrease in tourism caused by epidemic disease is intolerable. The extensive serological crossing that occurs among dengue viruses and between dengue viruses and other flaviviruses can be very confusing epidemiologically.