Dengue fever is an acute, mosquito-transmitted viral disease characterized by fever, headache, arthralgia (severe retro-orbital pain), myalgia, rash, nausea, and vomiting. Infections are caused by any of the four closely related, but antigenically distinct virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4). Infection with one of these serotypes does not provide cross-protective immunity, so persons living in a dengue-endemic area can have four dengue infections during their lifetimes. Dengue is primarily an urban disease of the tropics, and the viruses that cause it are maintained in a cycle that involves humans and Aedes aegypti, a domestic, day-biting mosquito that prefers to feed on humans. Although most dengue infections result in relatively mild illness, some can produce Dengue Hemorrhagic Fever (DHF) or dengue shock syndrome, with children being particularly at risk. Although epidemic outbreaks have been reported since 1779, the incidence has been increasing, with global, multiple serotype pandemics intensifying within the last 15 years. There is no specific antiviral therapy for dengue, but for both classical dengue and dengue hemorrhagic fever, symptomatic and supportive measures are effective. Important risk factors for DHF include the strain and serotype of the virus involved, as well as the age, immune status, and genetic predisposition of the patient.