Dengue infection, one of the most important mosquito-borne viral diseases of humans, is now a significant problem in several tropical countries. The disease, caused by the four dengue virus serotypes, ranges from asymptomatic infection, undifferentiated fever, dengue fever (DF) to severe dengue hemorrhagic fever (DHF) with or without shock. DHF is characterized by fever, bleeding diathesis and a tendency to develop a potentially fatal shock syndrome. Hematological findings include vasculopathy, coagulopathy and thrombocytopenia as the most constant findings. During the last twenty-five years, there have been increasing reports of dengue infection with unusual manifestations, mainly with cerebral and hepatic symptoms. Laboratory diagnosis includes virus isolation, serology and detection of dengue ribonucleic acid. Successful treatment, which is mainly supportive, depends on early recognition of the disease and careful monitoring for shock. Prevention depends on control of the mosquito vector. More efforts must be made to understand the pathogenesis of DHF in order to develop a safe and effective dengue vaccine.