A surprisingly high percentage of the population will experience at least one traumatic event in their lifetime (trauma being defined as a frightening situation in which one experiences or witnesses the threat of death or injury). Although not all individuals exposed to traumatic events will develop psychopathology—in fact, most do not—a significant minority will, with potentially devastating consequences for them and their loved ones.

Posttraumatic stress disorder (PTSD) has a prevalence rate of 7–8%, with even higher rates for specific subpopulations (e.g., military personnel). It is a disorder with significant impact on functioning and quality of life and should be diagnosed and treated according to the best available evidence.

This chapter covers the clinical presentation of PTSD, including comorbidities and suicidality as well as its underlying risk factors and neurobiology.

The first modern conceptualization of posttraumatic stress symptoms was described in 1678 as nostalgia and attributed to homesickness on the part of soldiers. Nearly two hundred years later, advances in modern weaponry contributed to such a large proportion of American Civil War soldiers exhibiting stress-related ailments—soldier's heart—that the first military hospital for the insane was established. Further advances in weapon technology in the First World War led to the proposed etiology of brain concussion caused by exploding shells, and hence the term shell shock. Other conceptualizations of posttraumatic symptoms at that time included irritable heart (overstimulation of the sympathetic nervous system) and war neurosis (Freud's suggestion that soldiers were reconciling their traumatic experiences in their minds). By the end of World War I posttraumatic stress was no longer attributed to physical brain injury, and by World War II the term battle fatigue had emerged, again with the implication that it represented weakness.

It is common for patients with PTSD to have a psychiatric history prior to exposure to a traumatic event; however, it is also common for a comorbid disorder to be diagnosed subsequent to onset of PTSD. Some argue that the rates of comorbidity in PTSD are artificially high owing to the degree of symptom overlap between PTSD and depression/other anxiety disorders. This is an important consideration warranting further investigation, though from a clinical practice perspective it may be most important to recognize the symptoms that patients experience, regardless of the disorder to which they might be attributed.