Research on natural and human-caused disasters strongly suggests that the psychological reactions following human-caused disasters, such as terrorism, are more intense and more prolonged than psychological reactions following natural disasters. Terrorists derive their power from their ability to psychologically injure, manipulate, and control the behavior of individuals and populations. In order to effectively understand, prevent, and respond to weapons of mass destruction and terrorist events, the centrality of their psychological impact must be understood. Certain characteristics of disaster increase the magnitude and severity of psychological effects. Terrorist events include the following of these psychologically dangerous event characteristics: lack of warning, lack of familiarity with type of event, sudden contrast of scene, serious threat to personal safety, scope of destruction, and exposure to gruesome situations. Other characteristics of terrorist events are intentional human causality, intensity of emotions and psychological reactions, degree of uncertainty, lack of control, deteriorated health status, disrupted social support systems, the duration of the event, symbolism of the terrorist target, and the fact that the entire community is affected. The psychological reactions to be anticipated immediately after the event for the general public are shock and disbelief; and for the rescue workers, anger and physical stress symptoms. Long-term reactions for both the public and responders are grief and bereavement, post-traumatic stress disorder, and panic disorders. Consultation, collaboration, and planning are needed among all mental health resources (local, State, Federal, government, private, and nonprofit) to ensure adequate and appropriate mental health response. 13 references