Theories on the aetiology of pathological anxiety abound. A critical review is given of the most influential apporaches (e.g. psychonalytical, “somatogenic” behavioural, psychophysiological and “biological theories), with emphasis on panic and agoraphobic disorders. Eviudence is presented from epidemiological and genetic research and from observations on the course of illness. A surprisingly constant prevalence of anxiety syndormes, and a familial distribution suggesting a pivotal importance of genetic factors, speak in favour of a biological model. The course of illness, however, points to the importance of environmental influences as triggering factors, and to congnitive and behavioural mechanisms for the perpetuation of the symptoms. Treatment responses hitherto documented support the biological and behagioural concepts, but the cognitive and psychophysiological theories are also supported to some extent. An attempt is made to combine these findings with biochemical and pharmacological findings in an intergrated model of panic and agoraphobia. This model takes the form of a vicious circle, and is compatible with biological and neuropharmacological as well as evolutionary and psychological con