PURPOSE OF REVIEW: Many potentially life-threatening infections cause fever. Several recent large studies help to define causes of fever in returned travelers. RECENT FINDINGS: The destination of travel determines the relative likelihood of the different major causes of fever. Systemic febrile illness occurs disproportionately among ill travelers returning from sub-Saharan Africa. Malaria remains the most important overall cause of systemic febrile illness in travelers to tropical regions; dengue fever is now the most prominent cause of fever in travelers to certain regions, most notably Asia. Chikungunya fever has emerged as a major cause of fever in travelers to Indian Ocean islands off Africa and to India itself. Causes of fever vary by the time of presentation after travel. Vivax malaria is an important cause of fever with onset more than a month after return; recently studies have shown that parasites causing relapse are genetically distinct from those causing primary infection. At expert referral centers up to 25% of febrile patients have no specific cause of fever determined. SUMMARY: Knowledge of predominant causes of febrile infections by geographic region, traveler characteristics, and time of presentation can assist the clinician in guiding posttravel diagnosis and empiric therapy of ill returned travelers and is also valuable in pretravel preparation. © 2007 Lippincott Williams & Wilkins, Inc.