Complex post-traumatic stress disorder (CPTSD) is a stress-related mental disorder theoretically happening in response to complex traumas, i.e. generally prolonged or repetitive exposures to a series of traumatic events, within which individuals perceive few or no chance to escape.

In the ICD-11 classification, CPTSD is a category of post-traumatic stress disorder (PTSD) with three additional clusters of significant symptoms: emotional dysregulations, negative self-beliefs (e.g. feelings of shame, guilt, failure for wrong reasons), and interpersonal difficulties. Examples of CPTSD's symptoms are prolonged feelings of terror, worthlessness, helplessness, distortions in identity or sense of self, and hypervigilance. CPTSD's symptoms share some similarities with the observed symptoms in borderline personality disorder, dissociative identity disorder and somatization disorder.

There exist strong relationships between CPTSD and repetitive adverse childhood experiences, especially among survivors of harmful foster care. In fact, the trauma model of mental disorders associates CPTSD with chronic or repetitive: sexual, psychological, physical abuse or neglect, intimate partner violences, bullying, kidnapping and hostage situations, indentured servants, slavery or other human trafficking, sweatshop workers, prisoners of war, concentration camp survivors, solitary confinement, defectors from authoritarian religions. The undergone situations generally last during long periods of time. Besides any situations involving captivity or entrapment (i.e. perceived situations lacking of easy and viable escape routes) can lead to CPTSD.