An assessment was conducted of the impact of infectious diseases on the 697,000 U.S. troops deployed to the Persian Gulf during 1990-1991 in Operations Desert Shield and Desert Storm. The incidence of nonbattle injuries, including infectious diseases, during this conflict was lower than during previous wars involving U.S. military personnel. The major reported causes of morbidity were generally mild cases of acute diarrheal and upper respiratory disease. The most unexpected outcome was the lack of arboviral infections, particularly sandfly fever, and the occurrence among U.S. troops of 12 cases of visceral leishmaniasis due to Leishmania tropica. The fact that infectious diseases were not a major cause of lost manpower, in sharp contrast to the experience among military personnel in World War II, can be attributed to a combination of factors: the presence of a comprehensive infrastructure of medical care, extensive preventive medicine efforts, and several fortuitous circumstances. Beneficial conditions that may not be present in future conflicts in this region include isolation of most combat troops to barren desert locations during the cooler, winter months, which provided the least favorable conditions for transmission of arthropod-borne diseases.