This paper summarizes the results of systematic studies published in peer-reviewed journals from 1999 to 2002 addressing post-traumatic stress reactions in children after mass disasters. Children's post-traumatic reactions are considered in five different contexts--natural disasters, large-scale human-induced accidents, spree shootings, war, and terrorism. Association of these reactions with gender and age, as well as longitudinal course, is addressed. Other post-traumatic reactions in children after a mass disaster, as well as the comorbidity of these with stress reactions, are reported. With this as background, the most relevant epidemiologic investigations conducted after the World Trade Center attacks are then described. It is expected that new knowledge in the area of children's post-traumatic reactions to disasters will result from the research initiatives launched after September 11, 2001.