Overall, 3% to 19% of travelers to the developing world will return to the United States with fever or will develop fever within weeks of their return. When evaluating the returning traveler with fever, it is important to know which pretravel immunizations the patient received; which medications he or she took during travel; the likely pathogen exposures during travel; and the incubation interval between travel and onset of fever. A physical examination that includes a search for focal findings may narrow the list of possible infections. Fever compatible with a common illness that occurs in the United States (e.g., mononucleosis) should always be considered. If the patient has fever without a focus and a tropical infection is suspected, malaria, dengue fever, and typhoid fever are common causes. These infections may appear clinically similar, with symptoms of fever, headache, muscle pain, joint pain, and malaise, and decreased white blood cell and platelet counts. Malaria can usually be diagnosed with a thin blood smear. Dengue fever is a clinical diagnosis. Serologic testing for dengue virus immunoglobulin M and G and virus detection tests can be performed to confirm the diagnosis, but are not immediately available. Typhoid fever can usually be diagnosed with a blood, urine, or stool culture.