Just more than 2,000 cases of Plasmodium falciparum malaria are reported in the United Kingdom annually, with a mortality rate of approximately 1%. Some studies suggest that patients with malaria who originate from disease-endemic areas are less likely to develop severe disease; such patients are often treated at home. We have prospectively examined 99 patients with imported P. falciparum malaria and categorized them according to severity as defined by World Health Organization criteria. There was no significant difference between those who developed severe disease and those who did not in terms of their ethnicity, residence in a malaria-endemic area, or history of previous episodes of malaria. To assume a patient has clinical immunity to malaria simply because they originate from or have lived for a long time in a malaria-endemic area may be inappropriate and unsafe.