Research on ontological security in International Relations (IR) has grown significantly in recent years. However, this scholarship is marked by conceptual ambiguity concerning the meaning of and relationship between the key concepts of ontological insecurity and anxiety. In addition, ontological security scholarship has been criticized for applying a concept that was originally developed for understanding individuals to states, and for being excessively concerned with continuity while largely ignoring change or seeing it as a negative force to be avoided. Despite such issues, however, reflection on the theoretical origins of ontological security remains limited. Based on such reflection, the present article argues that these issues can be circumvented if we return to one of the theoretical precursors of ontological security studies, the existentialist literature on anxiety. R.D. Laing, who coined the term ontological security, was strongly influenced by the existentialist anxiety theorists. Anthony Giddens, however, who drew on Laing and whose understanding of ontological security permeates IR scholarship, explicitly rejected the distinction between normal and neurotic anxiety, which was central to the work of existentialists like Rollo May. This article reintroduces this distinction. Doing so is useful, the article argues, both for providing conceptual clarity and for moving beyond the criticisms of ontological security mentioned above. More generally, the article suggests that ontological security studies has much to gain from drawing on the insights of the existentialist literature on anxiety to a greater extent than has hitherto been the case.