Diagnosis
PTSD can be difficult to diagnose, because of:

the subjective nature of most of the diagnostic criteria (although this is true for many mental disorders);
the potential for over-reporting, e.g., while seeking disability benefits, or when PTSD could be a mitigating factor at criminal sentencing
the potential for under-reporting, e.g., stigma, pride, fear that a PTSD diagnosis might preclude certain employment opportunities;
symptom overlap with other mental disorders such as obsessive compulsive disorder and generalized anxiety disorder;
association with other mental disorders such as major depressive disorder and generalized anxiety disorder;
substance use disorders, which often produce some of the same signs and symptoms as PTSD; and
substance use disorders can increase vulnerability to PTSD or exacerbate PTSD symptoms or both; and
PTSD increases the risk for developing substance use disorders. the differential expression of symptoms culturally (specifically with respect to avoidance and numbing symptoms, distressing dreams, and somatic symptoms)

Screening
There are a number of PTSD screening instruments for adults, such as the PTSD Checklist for DSM-5 (PCL-5) and the Primary Care PTSD Screen for DSM-5 (PC-PTSD-5).There are also several screening and assessment instruments for use with children and adolescents. These include the Child PTSD Symptom Scale (CPSS), Child Trauma Screening Questionnaire, and UCLA Post-traumatic Stress Disorder Reaction Index for DSM-IV.In addition, there are also screening and assessment instruments for caregivers of very young children (six years of age and younger). These include the Young Child PTSD Screen, the Young Child PTSD Checklist, and the Diagnostic Infant and Preschool Assessment. Assessment
Evidence-based assessment principles, including a multimethod assessment approach, form the foundation of PTSD assessment.
It was officially recognized by the American Psychiatric Association in 1980 in the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III). Symptoms
Symptoms of PTSD generally begin within the first three months after the inciting traumatic event, but may not begin until years later. In the typical case, the individual with PTSD persistently avoids either trauma-related thoughts and emotions or discussion of the traumatic event and may even have amnesia of the event. However, the event is commonly relived by the individual through intrusive, recurrent recollections, dissociative episodes of reliving the trauma ("flashbacks"), and nightmares (50 to 70%). While it is common to have symptoms after any traumatic event, these must persist to a sufficient degree (i.e., causing dysfunction in life or clinical levels of distress) for longer than one month after the trauma to be classified as PTSD (clinically significant dysfunction or distress for less than one month after the trauma may be acute stress disorder). Some following a traumatic event experience post-traumatic growth. Associated medical conditions
Trauma survivors often develop depression, anxiety disorders, and mood disorders in addition to PTSD.Substance use disorder, such as alcohol use disorder, commonly co-occur with PTSD. Recovery from post-traumatic stress disorder or other anxiety disorders may be hindered, or the condition worsened, when substance use disorders are comorbid with PTSD. Resolving these problems can bring about improvement in an individuals mental health status and anxiety levels.In children and adolescents, there is a strong association between emotional regulation difficulties (e.g.