Humanitarian workers face a significant risk of infection due to potential prolonged exposure and difficult living conditions. During the first quarter of 2007, a questionnaire regarding the occurrence of contracted infectious diseases and vaccinations was completed by 78 humanitarian expatriates from the French nongovernmental organization Médecins du Monde. We present the incidence of the most common infectious diseases calculated from this sample. For episodes of diarrhea, we found an incidence of 183 per 1,000 person-years; for malaria, 116 per 1,000 person-years; for typhoid fever, 30 per 1,000 person-years; and for tuberculosis, 12 per 1,000 person-years. Reported vaccination coverage rates were 100% for tetanus, 98% for diphtheria and polio, 91% for hepatitis B, but only 86% for typhoid and 78% for hepatitis A. By complying with the requirement for employers to conduct a risk assessment and record the results in the “single document,” Médecins du Monde could, through the implementation of an action plan, improve the prevention and management of infectious disease risks among humanitarian workers. (R.A.)