Preliminary evidence suggests that a significant minority of aid workers had a prior history of psychological disorder, with depression, anxiety disorders, and posttraumatic stress disorder (PTSD) being common. These factors that existed prior to employment as an aid worker may predict later symptoms of PTSD under the stressful conditions of aid work. The degree of professional experience prior to a particular international assignment is also an important factor in a person's ability to cope with the demands of an overseas mission. Untested idealistic views of disaster victims may lead to frustration and disillusionment when confronted by demanding, ungrateful victims who lie and steal in order to survive. Careful personnel selection and preparatory training can help prevent this factor as a cause of stress. Civil conflict, political instability, cultural differences, and poverty are common conditions of the working environment of the overseas aid worker. These conditions interacting with a worker's weak psychological resources, poor adjustment and coping skills, and an idealistic vision of being an instrument of change can lead to depression, anxiety, alcohol abuse, and PTSD at higher rates than the general population. These factors are aggravated by geographic, social, and/or cultural dislocation and isolation. What is required to prevent and counter these factors is a systematic, ongoing, and holistic response to psychosocial vulnerability of workers at all phases of aid employment. Organizational mechanisms should address preparation, mission support, and homecoming. 63 references