Unexpected extreme sudden traumatic stressor may cause post-traumatic stress disorder (PTSD). Important traumatic events include war, violent personal assault (e.g., sexual assault, and physical attack), being taken hostage or kidnapped, confinement as a prisoner of war, torture, terrorist attack, severe car accidents, and natural disasters. In childhood age sexual abuse or witnessing serious injuries or unexpected death of a beloved one are among important traumatic events.PTSD can be categorized into two types of acute and chronic PTSD: if symptoms persist for less than three months, it is termed "acute PTSD," otherwise, it is called "chronic PTSD." 60.7% of men and 51.2% of women would experience at least one potentially traumatic event in their lifetime. The lifetime prevalence of PTSD is significantly higher in women than men. Lifetime prevalence of PTSD varies from 0.3% in China to 6.1% in New Zealand. The prevalence of PTSD in crime victims are between 19% and 75%; rates as high as 80% have been reported following rape. The prevalence of PTSD among direct victims of disasters was reported to be 30%-40%; the rate in rescue workers was 10%-20%. The prevalence of PTSD among police, fire, and emergency service workers ranged from 6%-32%. An overall prevalence rate of 4% for the general population, the rate in rescue/recovery occupations ranged from 5% to 32%, with the highest rate reported in search and rescue personnel (25%), firefighters (21%), and workers with no prior training for facing disaster. War is one of the most intense stressors known to man. Armed forces have a higher prevalence of depression, anxiety disorders, alcohol abuse and PTSD. High-risk children who have been abused or experienced natural disasters may have an even higher prevalence of PTSD than adults.Female gender, previous psychiatric problem, intensity and nature of exposure to the traumatic event, and lack of social support are known risk factors for work-related PTSD. Working with severely ill patients, journalists and their families, and audiences who witness serious trauma and war at higher risk of PTSD.The intensity of trauma, pre-trauma demographic variables, neuroticism and temperament traits are the best predictors of the severity of PTSD symptoms. About 84% of those suffering from PTSD may have comorbid conditions including alcohol or drug abuse; feeling shame, despair and hopeless; physical symptoms; employment problems; divorce; and violence which make life harder. PTSD may contribute to the development of many other disorders such as anxiety disorders, major depressive disorder, substance abuse/dependency disorders, alcohol abuse/dependence, conduct disorder, and mania. It causes serious problems, thus its early diagnosis and appropriate treatment are of paramount importance.