A doctor or mental health professional diagnoses PTSD based on the symptoms described by the patient. Your doctor or mental health professional will perform a thorough psychological evaluation, asking you to describe the symptoms you are experiencing, when and how often they occur, and how intense they are. He or she may also ask you about the traumatic event that triggered your symptoms. You may also be given a physical examination to rule out other medical probems.

In order to be officially diagnosed with PTSD, you must meet certain criteria laid out in Diagnostic and Statistical Manual of Mental Disorders (DSM) published by the American Psychiatric Association. The criteria for diagnosis with PTSD are:

• You experienced or witnessed a traumatic event which involved death or serious injury (or the threat of same), or a threat to the physical integrity of oneself or others
• Your response to the event involved intense fear, helplessness, or horror (or in children: disorganized or agitated behavior).
• You persistently re-experience the event in one of the following ways:
• recurrent distressing thoughts, perceptions, or images of the event
• recurrent distressing dreams of the event
• Feeling as if the event were happening again through hallucinations or dissociate episodes (flashbacks) 
• Intense psychological distress or physical stress reaction upon exposure to things that remind you of the event
• You attempt to avoid situations, people, or things that remind you of the traumatic event or feel a sense of emotional numbness
• You have persistent symptoms of increased arousal (not present before the trauma), such as feeling “on edge” or hyper-vigilant for signs of danger, which may cause difficulty sleeping, irritability, or problems concentrating.
• Your symptoms last longer than one month
• Your symptoms cause significant distress or impairment in social situations, work, or other important areas of functioning.