International Classification of Diseases (ICD) - 10
Mental and behavioural disorders (F00-F99)
Neurotic, stress-related and somatoform disorders (F40-F48)
F43.1 Post-traumatic Stress Disorder
Arises as a delayed or protracted response to a stressful event or situation (of either brief or long duration) of an exceptionally threatening or catastrophic nature, which is likely to cause pervasive distress in almost anyone. Predisposing factors, such as personality traits (e.g. compulsive, asthenic) or previous history of neurotic illness, may lower the threshold for the development of the syndrome or aggravate its course, but they are neither necessary nor sufficient to explain its occurrence. Typical features include episodes of repeated reliving of the trauma in intrusive memories ("flashbacks"), dreams or nightmares, occurring against the persisting background of a sense of "numbness" and emotional blunting, detachment from other people, unresponsiveness to surroundings, anhedonia, and avoidance of activities and situations reminiscent of the trauma. There is usually a state of autonomic hyperarousal with hypervigilance, an enhanced startle reaction, and insomnia. Anxiety and depression are commonly associated with the above symptoms and signs, and suicidal ideation is not infrequent. The onset follows the trauma with a latency period that may range from a few weeks to months. The course is fluctuating but recovery can be expected in the majority of cases. In a small proportion of cases the condition may follow a chronic course over many years, with eventual transition to an enduring personality change (F62.0).
F43.1 Post-traumatic stress disorder
Diagnostic Criteria 
A. Exposure to a stressful event or situation (either short or long lasting) of exceptionally threatening or catastrophic nature, which is likely to cause pervasive distress in almost anyone.
B. Persistent remembering or "reliving" the stressor by intrusive flash backs, vivid memories, recurring dreams, or by experiencing distress when exposed to circumstances resembling or associated with the stressor.
C. Actual or preferred avoidance of circumstances resembling or associated with the stressor (not present before exposure to the stressor).
D. Either (1) or (2):
(1) Inability to recall, either partially or completely, some important aspects of the period of exposure to the stressor
(2) Persistent symptoms of increased psychological sensitivity and arousal (not present before exposure to the stressor) shown by any two of the following:
a) difficulty in falling or staying asleep;
b) irritability or outbursts of anger;
c) difficulty in concentrating;
e) exaggerated startle response
E. Criteria B, C (For some purposes, onset delayed more than six months may be included but this should be clearly specified separately.)
 Geneva, World Health Organization, 1992