This chapter focuses on the prevalence and etiology of anxiety disorders, including posttraumatic stress disorder (PTSD), following disasters. Recently a number of large national mental health surveys have estimated the prevalence of psychiatric disorders. The anxiety disorders that have been associated with disasters are generalized anxiety disorder, panic disorder, obsessive-compulsive disorder (OCD), social phobia, and specific phobia. The discussion of these matters is influenced by the fact that the conventions for recording patterns of comorbidity have changed between Diagnostic and Statistical Manual (DSM)-III and DSM-IV. The relationship between PTSD and the associated comorbidities with other anxiety and depressive disorders is important in determining the chronicity of morbidity following disasters. Anxiety disorders other than PTSD have been looked at in more detail in children, in part because of the potential developmental impact of disorders such as separation anxiety.