Complex PTSD (sometimes called "Disorder of Extreme Stress") is found among individuals who have been exposed to prolonged traumatic circumstances, especially during childhood, such as childhood sexual abuse. Developmental research is revealing that many brain and hormonal changes may occur as a result of early, prolonged trauma, and these changes contribute to difficulties with memory, learning, and regulating impulses and emotions. Combined with a disruptive, abusive home environment that does not foster healthy interaction, these brain and hormonal changes may contribute to severe behavioral difficulties (such as impulsivity, aggression, sexual acting out, eating disorders, alcohol/drug abuse, and self-destructive actions), emotional regulation difficulties (such as intense rage, depression, or panic attacks), and mental difficulties (such as extremely scattered thoughts, dissociation, and amnesia). As adults, these individuals often are diagnosed with depressive disorders, personality disorders, or dissociative disorders. Treatment often takes much longer than with regular PTSD; may progress at a much slower rate, and requires a sensitive and structured treatment program delivered by a trauma specialist.

Psychiatric disorders that commonly co-occur with PTSD include depression, alcohol/substance abuse, panic disorder, and other anxiety disorders. Although crises that threaten the safety of the survivor or others must be addressed first, the best treatment results are achieved when both PTSD and the other disorder(s) are treated together rather than one after the other. This is especially true for PTSD and alcohol/substance abuse.