OBJECTIVE: To assess self-reported health risk and risk-taking behavior of humanitarian expatriates. METHODS: A self-administered anonymous questionnaire was completed by International Committee of the Red Cross (ICRC) expatriates returning during May 2003 to September 2004, covering perceived health status before and after mission, malaria prevention, prevalence of exposure to stress, accidents and violence, and risk-taking behaviors. FINDINGS: More than one-third (36.4%) reported worse health on return from the mission. A third (35%) of expatriates returning from Sub-Saharan Africa excl. South Africa reported not having followed ICRC's recommendation on taking malaria prophylaxis in spite of stating a high degree of awareness of the risks and availability of effective drugs. Over 40% reported the mission having been more stressful than expected, mostly due to the working environment; 10% reported injury or accidents and 16.2% exposure to at least one act of violence. Almost one-third of the respondents reported having engaged in casual sexual relationships. Of these, 64% reported using condoms at every sexual contact, and women reported lower usage of condoms than men. Many (27%) reported involvement in risk-taking behavior. CONCLUSION: This study shows that humanitarian aid workers experience significant worsening of their health during overseas missions. Many are at risk of experiencing violence, accidents, or injuries. Despite awareness of the risks, many expatriates engage in behaviors that could endanger their health. Improved selection of expatriate staff, training programs emphasizing areas of concern, strengthening social support locally, and follow-up in field may help to alleviate these problems.