Malaria remains an overwhelming problem in tropical developing countries, with 300 to 500 million new cases and 1.5 to 3.5 million deaths per year. Malaria is a potentially life-threatening disease for travelers to the tropics. Imported malaria is an important clinical problem in nonendemic areas of the world because of increasing numbers of travelers, overseas workers, and immigrants from endemic areas. According to the World Health Organization's criteria, the recognition of one or more of the following clinical features should raise the suspicion of severe malaria: cerebral malaria (unrousable coma), severe anemia (hemoglobin <5 g/dL), renal failure (serum creatinine >3 mg/dL), pulmonary edema or adult respiratory distress syndrome, hypoglycemia (glucose <40 mg/dL), circulatory collapse or shock, disseminated intravascular coagulation, repeated generalized convulsions, acidosis (pH <7.25), macroscopic hemoglobinuria, hyperparasitemia (>5 percent of the erythrocytes infested by parasites), or jaundice (bilirubin >3 mg/dL). Although only a small proportion of patients with malaria develops severe manifestations, these patients require the most urgent and intensive care. Mortality among patients with cerebral malaria, even when treated in modern intensive care units, exceeds 30%, and when complicated by the adult respiratory distress syndrome, it may approach 80%. Among travelers, mortality remains a serious issue because of failure to obtain and use preventive measures, delay in seeking medical attention, and misdiagnosis.