It is contended that the fear of being overwhelmed or annihilated is a correlate of Freud' traumatic moment, constitutes a basic danger, and should be included in the series of fear of loss of the object, loss of love, castration, and superego censure. Traumatic and signal anxiety are conceptualized as two points in a series of potential responses, and it is assumed that mental representations of the early state of helplessness (originally preverbal) can later be anticipated. Major implications of annihilation anxiety noted by Freud and later psychoanalysts are reviewed, and are found to reflect fears of disintegration of the ego and of the self. Though it has been cited many times, the concept is relatively undeveloped. Key factors which increase the likelihood of annihilation anxiety are identified as traumatic experiences, ego weaknesses, and threats to self-cohesion. The prevalence of annihilation anxieties at various levels of psychopathology, as compared with other anxiety contents, is reviewed.