A transient depersonalization syndrome was identified in nearly 1/3 of persons exposed to life-threatening danger (accident victims) and close to 40% of a group of hospitalized psychiatric patients. Although the syndrome was similar in these populations, mental clouding developed more commonly among patients and alertness was more prominent among accident victims. Anxiety was significantly associated with the development of depersonalization among psychiatric patients and was almost certainly a factor in its appearance among accident victims. This syndrome was a specific response to extreme danger or its associated anxiety.