Post-Traumatic Stress Disorder (PTSD) may develop after a person is exposed to one or more traumatic events, such as sexual assault, serious injury, or the threat of death. The diagnosis may be given when a group of symptoms, such as disturbing recurring flashbacks, avoidance or numbing of memories of the event, and hyperarousal continue for more than a month after the traumatic event.
Most people having experienced a traumatizing event will not develop PTSD. Women are more likely to experience higher impact events, and are also more likely to develop PTSD than men. Children are less likely to experience PTSD after trauma than adults, especially if they are under ten years of age. War veterans are commonly at risk to PTSD.
Source: http://en.wikipedia.org/wiki/Post_traumatic_stress_disorder
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