Post-traumatic stress disorder (PTSD) may arise when people experience a traumatic event such as death, threatened death, serious injury, or actual or threatened sexual violence.* 

This definition applies primarily to simple trauma, or exposure to one circumscribed traumatic event. By contrast, complex trauma may arise from exposure over time to prolonged, repeated trauma, such as physical or sexual abuse, neglect, or violence. The symptom pictures resulting from simple and complex trauma differ somewhat.