© Cambridge University Press 2001, 2011. In this chapter we review the prevalence and comorbidity of anxiety disorders in general, and where possible the specifics of separation anxiety disorder (SAD), generalized anxiety disorder (GAD), specific phobias, panic, social phobia, and panic disorder. There were too few reports of agoraphobia to make a reliable estimate. We have not included post-traumatic stress disorder (PTSD) and obsessive–compulsive disorder (OCD), because their status as anxiety disorders is a topic still being debated for the revision of the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994). Most recent studies have omitted overanxious disorder (OAD) after its omission from the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994), but we shall have something to say about OAD later on.